BIOL 120A Chapter 7: Chapter 7 Detailed Notes

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erinraven791

23 Aug 2016

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What is inheritance: the transmission of traits form parents to off springs. What are genes: the hereditary material, dna found in chromosomes is organized into units called genes. Define locus: a gene is a segment of dna molecule, and its location in a specific chromosome is called locus. Genes often existing in two other forms called: alleles. Gregor mendel was a famous scientist who performed experiments on peas to determine which plants bred true. Monohybrid cross is when you mate individuals that differed in only one trait. For each pair of traits studied, one allele masked, or was dominant over the other allele in the f1 generation. When gametes are formed the pair of hereditary factors become separated so each sex cell receive only one type of each factor. The actual appearance of a trait is known as a phenotype. A test cross involves mating with an unknown genotype to a homozygous recessive individual.

Related Questions

These all relate to exceptions to the inheritance patterns encountered by Mendel.â

Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?

Select the four correct statements.

-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios.

-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance.

-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance.

-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios.

-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios.

-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios.

-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon.

-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon.

Chromosome Mapping (determining the relative positions of genes on a chromosome) - This is a two point cross since it involves two loci on a chromosome.

Follow the directions for the crosses below involving 2 traits located together on the same chromosome (Drosophila Chromosome IV): eyeless and shaven bristles. Please only typed answer, no hand-written work or screen shots please.

1. a. Perform a monohybrid cross between a female fly with the eyeless mutation and a male fly with shaven bristles. Show results for the F₁ offspring. (NOTE: You will use an F₁ female in the next cross.)
ENTER DATA HERE:

Question: Are the phenotypes of the F₁ offspring what you would have predicted for this cross: why or why not?

Question: After looking at your F₁ offspring, which allele is dominant: wild-type eyes or eyeless? How can you tell?

Question: After looking at your F₁ offspring, which allele is dominant: wild-type bristles or shaven bristles? How can you tell?

Draw the Chromosome IV pair of an F₁ offspring: (HINT: One chromosome was inherited from the mother, with the eyeless allele at the eye shape location (locus) and the wild-type allele at the bristles locus. The second chromosome was inherited from the father, with the wild-type allele at the eye shape locus and the shaven bristle allele at the bristles locus.)

1. b. Perform a testcross between an F₁ female offspring from the previous cross and a new male with both the eyeless and the shaven bristle traits to produce an F₂ generation.
ENTER DATA HERE:

Question: What phenotypes are found in the F₂ offspring?

Question: Are the phenotypes of the F₂ offspring what you would have predicted for this cross: why or why not?

Draw the 2 different Chromosome IV pairings you expected in an F₂ offspring: (HINT: The F₁ female will donate one or the other of the chromosomes you drew above to each offspring. The new male with both the eyeless and the shaven bristle traits can only donate one type of chromosome, with both mutations.)

Question: What are the 2 phenotypes that would result from the 2 different chromosome pairings you just drew?

Question: What are the other 2 phenotypes that you obtained in your F₂ offspring? What process, which occurred during meiosis, was responsible for the creation of these recombinant phenotypes?

Draw a map that shows the map distance (in map units or centimorgans) between the locus for the shaven bristle allele and the locus for the eyeless allele. (NOTE: You need to add the proportion of SV;EY flies to the proportion of wild flies OR add the number of SV;EY flies and wild flies and then divide by the total number of flies. Then multiply either number times 100.)âSHOW ALL CALCULATIONS BELOW

CALCULATIONS:

CHROMOSOME MAP:

There are several different ways to draw maps of the chromosomes. You can draw a simple line graph using a free online graphing tool, such as:

http://www.onlinecharttool.com/

http://nces.ed.gov/nceskids/createagraph/

Or you can simply use your keyboard to create a line with the dash or underline, with the abbreviations for the genes inserted, and then put the map units below, such as:

___________A_____________________B_________

50 map units

If an organismâs diploid chromosome number is 18, how many different possible combinations of homologous chromosomes lining up during meiosis exist for the eggs or sperm produced by that organism?

	A.	512
	B.	9
	C.	18
	D.	128
	E.	36

At the end of metaphase I, _______________ separate.

	A.	sister chromatids
	B.	germ cells
	C.	homologous chromosomes
	D.	haploid chromatids
	E.	centrioles

Mendel observed that dominant traits

	A.	are seen in all of the F1 hybrid pea plants in his experiments.
	B.	are expressed in all plants.
	C.	were absent in the F1 generation of pea plants that he used in his experiments.
	D.	were the only traits seen in the F2 generation of pea plants in his experiments.
	E.	are only expressed in hybrids.

Cytokinesis in plant cells differs from cytokinesis in animal cells because

	A.	there is no difference.
	B.	in plant cells, the cell plate must also divide into two parts.
	C.	the contractile protein, actin, is important only in plant cells.
	D.	plant cells have a rigid cell wall.
	E.	a contractile ring forms only in plant cells.

Sickle cell anemia is an example of what type of inheritance?

	A.	complete dominance
	B.	incomplete dominance
	C.	codominance
	D.	multiple alleles
	E.	recessive dominance

Which of the following statements is true:

	A.	The dominant allele is masked in homozygous dominant individuals.
	B.	With recessive genetic disorders, if both parents are carriers, the offspring will all be affected.
	C.	In carriers, the recessive allele causes an intermediate phenotype.
	D.	In recessive genetic disorders, the mother and/or father of an affected individual must also be affected.
	E.	With dominant genetic disorders, the mother and/or father of an affected individual must also be affected.

Skin cancers typically develop in the

	A.	upper layers of the epidermis.
	B.	lower layers of the dermis.
	C.	subcutaneous layer.
	D.	lower layers of the epidermis.
	E.	upper layers of the dermis.

Duchenne muscular dystrophy (MD) is inherited from an X-linked recessive allele. What is the probability that a son with Duchenne MD inherited this disease from his biological father?

	A.	1/2
	B.	0
	C.	1/16
	D.	1/4
	E.	1/8

The genetic makeup of a particular trait in an individual is its

	A.	genotype.
	B.	heterozygosity.
	C.	phenotype.
	D.	filial.
	E.	dominance.

What structure holds the sister chromatids to the spindle fibers?

	A.	chromatin
	B.	kinetochore
	C.	MPF
	D.	centromere
	E.	cyclin

If you view a cell in which the genetic material is beginning to be visible as separate bodies, and the nucleus has disappeared from view, you may surmise that the cells is in

	A.	telophase.
	B.	anaphase.
	C.	interphase.
	D.	metaphase.
	E.	prophase.

Gregor Mendel was successful in his analysis of the genetics of pea plants because

	A.	he examined and analyzed both the F1 and F2 generations.
	B.	he studied the parental plants to determine their differences.
	C.	he decided to only look at his results in an objective manner.
	D.	he studied a trait that had a strange inheritance pattern.
	E.	pea plants have genetics different from other organisms.

Tall corn plants (T) are dominant to dwarf plants (tt). Solid green leaves (G) are dominant to leaves with a white tip (gg). A cross between two corn plants yielded the following phenotypes: 51 tall plants with a white tip on their leaves; 43 dwarf plants with solid leaves; 48 dwarf plants with white tips on their leaves; 45 tall plants with solid leaves. What are the genotypes of the parents that produced these plants?

	A.	None of the above
	B.	TtGg x Ttgg
	C.	ttGG x TTgg
	D.	TtGg x TtGg
	E.	TtGg x ttgg

In humans, a gene that has been identified as causing a type of skin cancer is the

	A.	superwoman echidna.
	B.	mutant superman.
	C.	sonic hedgehog.
	D.	mutant mole rat.
	E.	superhero aardvark.

The segregation principle states that in sexually reproducing diploid organisms the two copies of each gene

	A.	segregate from each other during meiosis.
	B.	must always be the same allele.
	C.	separate from each other during mitosis.
	D.	will both wind up in either the sperm or egg.
	E.	move together as a unit during meiosis.

In what phases is the genetic material in the cell correctly referred to as chromatids?

	A.	metaphase and telophase
	B.	anaphase and metaphase
	C.	interphase and telophase
	D.	interphase and prophase
	E.	metaphase and prophase

Consider two traits for an organism, determined by two genes, each of which is governed by at least two alleles. In the case of a dihybrid individual, the gametes formed will be of either the parental type or the recombinant type. Recombinant type gametes are formed because of

	A.	the principle of dihybrids.
	B.	multiple alleles.
	C.	heterozygosity.
	D.	incomplete dominance.
	E.	independent assortment.

An allele is

	A.	an alternate form of a gene.
	B.	always recessive.
	C.	the main factor determining a trait.
	D.	always one of a pair.
	E.	the dominant form of a gene.

After the DNA is replicated, and it condenses in prophase, two identical rods of DNA are seen. These are

	A.	spindle fibers.
	B.	kinetochores.
	C.	chromatids.
	D.	chromatin.
	E.	centromeres.

Special cells found in the gonads that give rise to gametes upon division are called

	A.	egg cells.
	B.	somatic cells.
	C.	germ cells.
	D.	stem cells.
	E.	basal cells.

BIOL 120A Chapter 7: Chapter 7 Detailed Notes

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