BIOL10005 Lecture Notes - Lecture 8: Centimorgan, Sister Chromatids, Meiosis

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jadebutterfly872

29 Jun 2018

School

University of Melbourne

Department

Biology

Course

BIOL10005

Professor

All

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Lecture 8: Autosomal Linkage

Dihybrid ratios:

9:3:3:1 (complete dominance)

9:7 = A; - B;

9:6:1 = A;-B- and aa;bb

15:1 = everything vs aa;bb

13:3 = everything vs aa;B-

Types of crosses:

Reciprocal crosses: determine whether it's sex linked

oDifferent outcome = sex linked

Test cross to homozygous individual: assorting independently or autosomal linked

oHomozygous does not contribute to the phenotype --> constant

oSee what other parent contributes

Back cross: offspring back to a parent

oTo determine genotype of parent

Independent assortment:

Chromosomes pairs behave independently of each other and assort into gametes of equal

frequency

Genes on separate chromosome or far enough away from each other

Autosomal linkage:

Genes on same chromosome --> independent segregation of alleles may not occur

Doesn't assort independently

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Document Summary

Reciprocal crosses: determine whether it"s sex linked: different outcome = sex linked. Test cross to homozygous individual: assorting independently or autosomal linked: homozygous does not contribute to the phenotype --> constant o. Back cross: offspring back to a parent. Chromosomes pairs behave independently of each other and assort into gametes of equal frequency. Genes on separate chromosome or far enough away from each other. Genes on same chromosome --> independent segregation of alleles may not occur. During meiosis: crossing over (chiasma) takes place o. Exchange (recombination) of maternal + paternal chromatids occur. Crossing over between sister chromatids --> no genetic difference. Recombination: recombining between paternal + maternal --> not sister o. Frequency of recombination = measure of relative distance between gene loci o. The closer the two genes = the lower the frequency of recombination: genes further apart = recombines more frequently o o. If more than 50 mu --> assort independently.

Related Questions

Which of these statements is incorrect?

Syntenic genes are located on the same chromosome.

Independent assortment results in recombinant chromosomes.

You can reliably predict the relative genetic distance fromgenesâ physical distance on a chromosome.

Linked genes are always syntenic.

What is the relative genetic distance between two linked genesif the recombination frequency is 0.49?

0.49 cM

4.9 cM

49 cM

490 cM

What statement best explains the distortion in Mendelian ratiosobserved by Bateson & Punnett in 1905? (Reminder: they found anoverrepresentation of F2 offspring showing both dominant orrecessive phenotypes, and an underrepresentation of offspringdisplaying one dominant and one recessive phenotype)

Human error: they should have been more careful about theirexperimental setup.

Gene linkage: Genes for flower color and pollen shape arephysically close on the same chromosome, leading to a breakdown inthe independent assortment of the alleles for these traits.

Chromosome crossover: Homologous recombination of twochromatids during meiosis caused the alleles to shuffle, resultingin a breakdown of the independent assortment of the alleles forthose genes.

Random variation: No two situations are alike. In finitepopulations, you are going to get some variation across a mean.

When determining the relative genetic distance between twogenes, why is dihybrid back-cross preferable over traditionaldihybrid cross?

9:3:3:1 phenotypic ratio is easier to work with than 1:1:1:1ratio.

Genotypes of the offspring can be determined based on theirphenotype.

If the genes are independently assorted, the dihybrid back-crosswould result in only 2 genotypes in the F1 generation.

B and C

Why do we map genes?

To understand how genes interact with each other

Comparative genomics analysis

To determine the genotype of an organism

All of the above

coralox210

What is a genome? What is a genome made of? Describe the bacterial genome. How do bacteria reproduce? What is binary fission? Distinguish between a chromosome and chromatin. Where are chromosomes located in eukaryotic cells? What is the chromosome made of? What is a centromere? What is the centromere's role? What are sister chromatids and how do they arise? Distinguish between somatic cells and germ (gametes) cells. Describe the cell cycle. What are the different phases? What occurs during S phase? What is interphase? How is the cell cycle controlled?

Describe mitosis. What are the phases of mitosis? What occurs in each of the phases of mitosis? What is cytokinesis? How does this differ between plant and animal cells? What is a kinetochore? Where does it form? What is its role? What is the role of microtubules in mitosis? What is a centriole and what is it composed of? What is a centrosome and what is its role in mitosis? What is the metaphase plate and why is this important? What is the mitotic spindle, its role and its makeup? What defines a diploid cell? How many copies of each chromosome is in a diploid cell? What about a haploid cell? Why do the daughter cells of mitosis always have the same complement of chromosomes?

Describe meiosis. What are the phases of meiosis? What occurs in each of the phases of meiosis? Distinguish between meiosis I and meiosis II and describe how each of these processes compare to mitosis. Why do animal cells undergo meiosis? What is a gamete? What is a zygote? What are recombination, crossing-over, and chiasma? When and why does this occur? What is meant by 'homologous pair of chromosomes'? Why don't the daughter cells of meiosis have the same genetic makeup? What controls the segregation of chromosomes into the gametes?

What are genetic characters? What are genetic traits? What is an allele? What is a locus? How many alleles at each locus would a human cell have and why? Distinguish between genotype and phenotype. What is meant by a dominant gene? What is meant by a recessive gene? How do these differ? What is the genotype of a homozygous dominant organism? What is its phenotype? What is the genotype of a homozygous recessive organism? What is its phenotype? What is the genotype of a heterozygous organism? What is its phenotype? What is a genetic cross? Distinguish between the P, F1, and F2 generations. What is a true-breeding line? What is the genotype and phenotype of a cross between homozygous dominant and homozygous recessive parents? If the F1 progeny are crossed, what would be the genotype and phenotype of the F2 generation? What would be the phenotypic ratio? What would be the genotypic ratio? Be ready to generate Punnet square tests or probability analyses of crosses involving more than one genetic locus. Describe a dihybrid cross where two alleles are homozygous dominant in one parent and homozygous recessive in the other. What would be the phenotypic ratio of the F2 generation from this dihybrid cross? What is meant by independent assortment? Be prepared to calculate probabilities resulting from different crosses.

Distinguish between complete and incomplete dominance. How would incomplete dominance alter the results of a hybrid cross? What would the resulting F2 generation phenotype and genotype ratios be? What is codominance? How does this affect the results of crosses? Be prepared to determine likely blood types of parents based on the blood types of their offspring. What is a polygenic trait? What is a carrier state for a genetic disease? What is meant by linked genes? How does this affect expected outcomes of genetic crosses? How is gene linkage used for chromosomal mapping? Distinguish between autosomes and sex chromosomes. What sex chromosomes are found in women? What sex chromosomes are found in men? What are sex-linked traits? Be prepared to give the results of crosses that involve sex-linked recessive traits. What is the process of nondisjunction? What are the likely results? Why is this important? What is a Barr body? Recognize the genetic abnormality of Downs Syndrome, Turner's Syndrome, and Klinefelter's Syndrome.

pucewallaby221

Please show detailed work. Thanks in advance.

16. Syntenic genes can assort independently when

A) they are very close together on a chromosome.

B) they are located on different chromosomes.

C) crossing over occurs rarely between the genes.

D) they are far apart on a chromosome and crossing over occurs frequently between the genes.

E) they are far apart on a chromosome and crossing over occurs very rarely between the genes.

17. The alleles of linked genes tend to

A) segregate together more often than expected by random assortment

B) assort independently.

C) be mutated more often than unlinked genes.

D) experience a higher rate of crossing over.

E) assort independently and show a higher rate of crossing over.

18. If you know that the frequency of recombination between genes X and Y is 34% and between X and Z is 25%, can you predict the order of the three genes?

A) Yes; the order is X-Z-Y.

B) Yes; the order is X-Y-Z.

C) Yes; the order is Z-X-Y.

D) No; based on this data alone, the order could be Z-Y-X or X-Y-Z.

E) No; based on this data alone, the order could be X-Z-Y or Z-X-Y.

Question 19 - 20. You have performed the following dihybrid cross in Drosophila using the black body color (b) and vestigial wing (vg) mutations. The b+ (grey body) and vg+ (normal wing) are dominant wild type alleles. These genes are autosomal.

Female â b+ vg+/b vg Ã male â b vg/b vg

Progeny:

Phenotype # of Progeny

Grey body normal wing 965

Black body vestigial wing 944

Grey body vestigial wing 208

Black body normal wing 195

19. Assuming linkage between black and vestigial, the estimated recombination frequency would be:

0.17

0.09

0.82

1.00

0.50

20. What key test could you use to determine whether the observed offspring frequencies deviate from those expected by chance alone?

A) Pascal's triangle

B) The product rule

C) The Chi-square (Ï²) test

D) The law of random assortment

E) The sum rule

21. In a genome wide association study (GWAS) designed to map the gene(s) that control height you divide subjects into a group of 1000 who are all more than seven feet tall and a control group of 1000 people of average height. You find the following associations between two genetic markers and the height trait:

		Tall group	Control group
Marker 1	Allele A	20%	50%
	Allele T	80%	50%

Marker 2	Allele G	15%	15%
	Allele C	85%	85%

What is your best guess for which marker is more closely linked to a gene that influences height?

A) Marker 1

B) Marker 2

22. Two pure breeding parents produce red and white flowers. They are crossed and the F1 produces pink flowers. When the F1 are selfed to produce the F2, nine distinct classes of pigmentation are present among F2 individuals. What is your best guess of the minimum number of genes that underlie flower pigmentation in this species?

A. 2

B. 3

C. 4

D. 5

E. 6

23. In a quantitative genetic experiment you identify two genes that confer bands of color on the back of a fly. At each gene, a dominant allele causes one band of color. If flies that are heterozygous at both loci are crossed, what ratio of offspring do you expect in each phenotype (i.e., number of color bands) class? (answer options are given from lowest to highest band number)

A) 1:1:1:1:1

B) 1:2:2:2:1

C) 1:4:6:4:1

D) 4:4:4:4:4

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BIOL10005 Lecture Notes - Lecture 8: Centimorgan, Sister Chromatids, Meiosis

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