BSC 2010C Lecture Notes - Lecture 15: X-Inactivation, Y Chromosome, Somatic Cell

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cerisegoose26

19 Apr 2018

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Thomas Morgan Hunt

Worked with fruit flies ("perfect model organism")

Has only four pairs of chromosomes (8 total)

3 pairs of autosomes and one pair of sex chromosomes

XX and XY

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Not much variety in traits

Fruit flies in captivity were "wild type" - phenotype most commonly

found in nature

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Bred white-eyed male fly to a wild-type female

All F1offspring had red eyes

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Bred an F1 female to an F1 male

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F2 offspring shows 3:1 ratio of red eyes

All females had red eyes

Of the males, 50% had red eyes and 50% had white eyes (sex linked

trait)

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Sex-Linked Traits and the Y chromosome

Y chromosome has a gene called SRY and it's responsible for testes

development

Without SRY, gonads develop into ovaries

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Y chromosome has 78 genes

Half are expressed in testes

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Nearly all of them are related to being male

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Males get all of their x chromosome genes from their mother

X chromosome has many genes and many of those are unrelated to sex

If a trait on the X chromosome is recessive

Female will express the trait only if she is homozygous recessive

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Males will express the trait if he receives a recessive allele from his mom

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X chromosome inactivation in females

Only one x is needed; females correct this by inactivating one X in every somatic

cell

Happens during embryonic development

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Which X is inactivated is random and independent

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Inactivated X becomes a Barr body

Barr bodies are only activated in ovaries for meiosis

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Inactivation occurs in methylating DNA of one X chromosome

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Pedigree Analysis

Allows tracking of genetic traits in family trees through multiple generations

Males are squares

Females are circles

Individuals affected are shaded

Horizontal line=mating

Vertical line= offspring

Chromosomal Basis of Inheritance

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Related Questions

In fruit flies, the gene for eye color is sex-linked (X-chromosome)and red eye color is dominant over white. The gene for body coloris an autosomal trait with gray dominant over black. A heterozygousred-eyed, pure-bred gray female mates with a heterozygous gray malewho has red eyes. What is the probability that any of the offspringproduced have he following traits? You must show your work (i.e.Punnett squares) to get credit.

a. Red eyes
b. gray body
c. white eyed female
d. white eyes and heterozygous gray body
e. female and red eyed gray body

peachzebra571

The following question is a sex-linked trait. Review the patterns of inheritance of sex-linked traits before answering the following questions. Make sure to indicate chromosomes and alleles in your answers when necessary.

Hemophilia is a caused by a recessive mutation found on the X chromosome in humans. The recessive allele (X^h) is associated with abnormal blood clotting (hemophilia), while the dominant allele (X^N) causes normal blood clotting.

A man with normal blood clotting and woman who is heterozygous are going to have a child. What is the probability of an offspring who is a carrier of hemophilia, and if so, the sex(es) of the offspring?

A. Chances are 25% of a son who is a carrier

B. There is no chance of an offspring who is a carrier

C. Chances are 50% of either a son or a daughter who is a carrier

D. All offspring, male or female, will be carriers

E. Chances are 1 in 4 of a daughter who is a carrier

2. Two fruit flies, one with red eyes and one with white eyes mate and have an offspring with white eyes. Having red eyes is a dominant trait (R) while white eyes (w) is recessive. Based on this information, what must be the genotypes of the parental white-eyed fruit fly and the parental red-eyed fruit fly?

A. Red-Eyed fruit fly: Rw

White-eyed fruit fly: ww

B. Red-Eyed fruit fly: RR

White-eyed fruit fly: wR

C. Red-Eyed fruit fly: R

White-eyed fruit fly: w

D. Red-Eyed fruit fly: rr

White-eyed fruit fly: wr

E. Red-Eyed fruit fly: RR

White-eyed fruit fly: ww

Genes located on mitochondrial DNA are usually inherited in whatfashion?
A. Randomly
B. From the mother
C. From the father
D. Evenly from both the mother and the father
E. By independent assortment

Wild type fruit flies have red eyes. A white-eyed female fly iscrossed with a red-eyed male fly. All of the females from the crossare red-eyed and all of the males, white-eyed. What type ofinheritance pattern is this?
A. Independent assortment
B. Autosomal dominant
C. Autosomal recessive
D. Incomplete dominance
E. Sex-linked on X chromosome

What fraction of the offspring of the cross AaBb

BSC 2010C Lecture Notes - Lecture 15: X-Inactivation, Y Chromosome, Somatic Cell

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