BME 80H Lecture Notes - Lecture 10: Homologous Chromosome, Meiosis, Gamete

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tealantelope800

11 Jun 2018

School

UCSC

Department

Biomolecular Engineering

Course

BME 80H

Professor

Wendy Rothwell

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10th lecture

3. Meiosis results in genetic variation (2 ways)

a) crossing over in prophase I

b) different pairing orientations at

metaphase I (figure 2.16a) The total

possible combinations is 2n where n =# of

homologous chromosome pairs.

-2 ^23

III. Genes as hereditary units

A. What are genes?

- Genes are located at specific positions (genetic

loci, locus sing.) along each chromosome (figure

15.4)

- Made up of stretches of particular nucleotide

sequence.

- Only make up approx. 1.5% of the genome.

B. Genes can take on alternative (variant) forms =

alleles

-you can see the whether they are AA or Aa or aa

by looking at the same locus

C. Explaining Mendel's observations via Meiosis (table

3.2, figure 3.12/3.10)

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1. One member of each homologous pair of

chromosomes, each with their genetic alleles,

segregates into the gamete

-First law: Segregation

2. The orientation of each pair of homologous

chromosomes has no effect on the pairing

orientation of another pair of homologues

-Law of Independent Assortment

a) consistent with Mendel (figure

3.12/3.10): Note the 4, equally likely

gametes resulting from meiosis in a

dihybrid individual

-look at figure 3.12 and know both

combinations are equally likely

-9331 ratio so if AaBb x AaBb you get 9: A-B-

3:A-bb 3:aaB- 1:aabb

b) not consistent with Mendel (Handout:

old figure 2.17) Linked genes (those close

together on the same chromosome) do not

assort independently.

-linked alleles tend to be inherited together

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Document Summary

10th lecture: meiosis results in genetic variation (2 ways, crossing over in prophase i, different pairing orientations at metaphase i (figure 2. 16a) the total possible combinations is 2n where n =# of homologous chromosome pairs. Genes are located at specific positions (genetic loci, locus sing. ) along each chromosome (figure. Made up of stretches of particular nucleotide sequence. 1. 5% of the genome: genes can take on alternative (variant) forms = alleles. You can see the whether they are aa or aa or aa by looking at the same locus: explaining mendel"s observations via meiosis (table. 3. 2, figure 3. 12/3. 10: one member of each homologous pair of chromosomes, each with their genetic alleles, segregates into the gamete. First law: segregation: the orientation of each pair of homologous chromosomes has no effect on the pairing orientation of another pair of homologues. Law of independent assortment: consistent with mendel (figure. 3. 12/3. 10): note the 4, equally likely gametes resulting from meiosis in a dihybrid individual.

Related Questions

1. Characters that show a continuous range of variation, such as height and eye color, usually are controlled:

a.	by a single gene with two alleles that are codominant.

b.	by many genes with an additive effect.

c.	by epistatic interactions between two genes.

d.	mainly by the environment, with only a small genetic component.

2. In humans, red-green colorblindness is inherited as a sex-linked recessive trait. In order for a woman to be red-green colorblind, which of the following statements must be true.

a.	Her mother must be red-green colorblind.

b.	All of her brothers must be red-green colorblind.

c.	Her father must be red-green colorblind.

d.	All of the above statements must be true if a woman is red-green colorblind.

3. The x-ray crystallography data collected by Rosalind Franklin suggested to Watson and Crick that the:

a.	structure of DNA is a double helix.

b.	two strands of the DNA molecule are joined by hydrogen bonds between the bases.

c.	four bases within DNA pair in a specific way.

d.	two strands of the DNA molecule are joined by covalent bonds between the bases.

4. In the genetic code, _________ one amino acid.

a.	one nucleotide specifies

b.	two nucleotides specify

c.	three nucleotides specify

d.	four nucleotides specify

5. During Meiosis I, a homologous pair of chromosomes may not separate, resulting in daughter cells that have extra chromosomes or are missing chromosomes. This can lead to genetic disorders, including Down Syndrome. This phenomenon is called:

a.	independent assortment.

b.	nondisjunction.

c.	segregation.

d.	crossing over.

6. You are a human geneticist studying the incidence of retinitis pigmentosa in the residents of Tristan de Cunha, a group of small islands in the middle of the southern Atlantic Ocean. The allele for retinitis pigmentosa, which causes a form of blindness, is inherited as an autosomal recessive. You have determined that the frequency of this allele (r) in the population is 0.4 (40%). Using the principles of the Hardy-Weinberg rule, you would estimate the frequency of individuals who are heterozygous for this allele (Rr) in the population to be:

a.	0.16 (16%)

b.	0.24 (24%)

c.	0.36 (36%)

d.	0.48 (48%)

7. Natural selection acts at the level of the:

a.	phenotype.

gene.

c.	population.

d.	nucleotide.

8. You are working with pea plants, trying to recreate the experiments that Mendel performed. You are doing a dihybrid cross with a plant that is heterozygous for both seed shape and seed color, with the genotype RrYy. Which allelic combinations would you expect to find in the gametes produced by this plant?

a.	This plant would produce only RY and ry gametes.

b.	This plant would produce only RrYy gametes.

c.	This plant would produce RY, Ry, rY, and ry gametes.

d.	You cannot determine which gametes this plant can produce without knowing the genotypes of its parents.

9. Biochemist Erwin Chargaff found that in DNA there is a special relationship between the four bases that we now call Chargaff's rule. His observation was that, in an organism's genome the:

a.	percentage of A nucleotides = the percentage of T nucleotides, and the percentage of C nucleotides = the percentage of G nucleotides.

b.	four bases all occur in an equal frequency (25%) within each organism.

c.	percentage of A nucleotides = the percentage of G nucleotides, and the percentage of C nucleotides = the percentage of T nucleotides.

d.	genetic material is composed of proteins, not DNA.

10. During DNA replication:

a.	each strand of the double helix acts as a template for the synthesis of a new strand.

b.	the enzyme DNA polymerase adds nucleotides to the strand being synthesized.

c.	the bases A,C,G and T are required.

d.	All of the above are true of DNA replication.

11. During translation, amino acids are joined by peptide bonds to make polypeptides. The formation of these peptide bonds is catalyzed by:

12. If an allele (R) at a gene with two alleles shows complete dominance, individuals with the genotypes ______ will have the same phenotype.

a.	RR and rr.

RR and Rr

Rr and rr

d.	Each of the three possible genotypes will have a different phenotype.

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BME 80H Lecture Notes - Lecture 10: Homologous Chromosome, Meiosis, Gamete

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