BIOL10005 Lecture Notes - Lecture 6: Karyotype, Color Blindness, Y Chromosome

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azurealpaca671

12 Jun 2018

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University of Melbourne

Department

Biology

Course

BIOL10005

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All

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Lecture 6 - Friday 5 August 2016

BIOL10005 - GENETICS & THE EVOLUTION OF LIFE

LECTURE 6

CHROMOSOMES & SEX DETERMINATION

CHAPTER 9 - INHERITANCE

SEX LINKAGE AND CHROMOSOMES

SEX LINKED GENES

•Sex linked genes are genes that are inherited differently in males and females.

•Heterozygous red and white eyes flies crossed (female and male respectively), F1 generation all

red eyed. F1 and F1 crossed and all the female F2s were red eyed and half of the males were white

eyed.

GENES ARE ON CHROMOSOMES

•Every organism has a characteristic set

of chromosomes. Most eukaryotes have

2 types of chromosomes; autosomes,

which are the same in morphology

(appearance) in males and females, and

sex chromosomes, which are different in

morphology and are present in different

numbers in males and females and are

involved in sex determination.

•(With the exception of gametes), cells in

animals and plants are generally diploid

cells, they contain pairs of autosomes,

one autosome of each chromosome type

inherited from each parent.

•These are termed homologous

chromosomes or homologs. Humans

have 22 pairs of homologs (therefore 44

autosomes) and one pair of sex

chromosomes (therefore 2 sex

chromosomes) in every somatic cell.

•The separation of homologs at meiosis

explains the segregation of alleles during

the formation of gametes.

•Most common sex chromosome pattern is for males to have an X

chromosome and a smaller Y chromosome and for females to have

2 X chromosomes. Both the female XX and the male Xy behave as

homologs. The Y chromosome doesn’t carry much genetic info.

•Sex linked genes are located on the X chromosome.

•Each female offspring receives either of her mother’s two X

chromosomes with equal probability but always inherits her

father’s single X chromosome. Each male offspring receives either

of his mother’s two X chromosomes with equal probability but

always inherits his father’s single Y chromosome.

•Having extra chromosomes muddles with the others.

X LINKED TRAITS IN HUMANS

•Most common X linked trait in humans is red-green colour

blindness. About 8% of Caucasian males have it. Probably because

the phenotype of colour blind allele is recessive and that the gene

for the blindness is on the X chromosome with no comparable gene !

Chromosomes are sorted from A to G

due to size & centromere position.

Karyogram

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Document Summary

Biol10005 - genetics & the evolution of life. Sex linked genes: sex linked genes are genes that are inherited differently in males and females, heterozygous red and white eyes flies crossed (female and male respectively), f1 generation all red eyed. F1 and f1 crossed and all the female f2s were red eyed and half of the males were white eyed. Chromosomes are sorted from a to g due to size & centromere position. Genes are on chromosomes: every organism has a characteristic set of chromosomes. Humans have 22 pairs of homologs (therefore 44 autosomes) and one pair of sex chromosomes (therefore 2 sex chromosomes) in every somatic cell: the separation of homologs at meiosis explains the segregation of alleles during the formation of gametes. Karyogram: most common sex chromosome pattern is for males to have an x chromosome and a smaller y chromosome and for females to have. Both the female xx and the male xy behave as homologs.

Related Questions

3. Consider a cross between white-eyed female flies and red-eyed male flies. Importantly, the white gene is X-linked. Write out the punnett square here. Be sure to define your allele symbols then indicate the probability (a ratio is fine) of observing any one of the following phenotypes:

a. Red-eyed females _________

b. Red-eyed males _________

c. White-eyed females ________

d. White-eyed males. __________

4. You want to build a double mutant (ab/ab) between two genes, A and B, that are 10 map units apart. You first cross a/a into b/b to create the dihybrid: a+/+b. Next, you do an F1 cross and search the F2 generation for the rare double mutant: ab/ab. What percent of the progeny (offspring) will have the double mutant phenotype in the F2 generation? Show your equation. 5. EXTRA CREDIT. It should be noted that white was not the first sex-linked mutation discovered. In the currant moth Abraxus, DONCASTER and RAYNOR (1906) described a trait called lacticolor segregating among wild females but not among males. How might one explain this?

fuchsiagerbil537

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

Drosophila has four pairs of chromosomes: the sex chromosomes (XX in the females; XY in the males) and three pairs of autosomes. You are studying a new mutant strain with blue eyes. You wish to know if blue eye colour is a dominant mutation and on which chromosome the blue eye locus can be found. When you cross a pure-breeding female blue-eyed fly with vestigial wings and spineless bristles to a male fly with wild type eye colour, wings, and bristles, all of the F1 progeny are completely wild type. An F1 male is backcrossed to a triple mutant female, producing the following progeny (remember that there is no crossing over in Drosophila males):

Wild type eyes, wings, and bristles:	72 females, 69 males
Wild type eyes and bristles, vestigial:	83 females, 77 males
Wild type wings, blue eyes, spineless:	60 females, 65 males
Blue eyes, spineless, vestigial:	62 females, 58 males

a. Is the mutation dominant or recessive? Explain.

b. Since you know that the locus for vestigial wings is on chromosome 2 and the locus for spineless bristles is on chromosome 3, what chromosome carries the locus for blue eyes? Show your work, including the step-by-step reasoning you used to arrive at your answer.

c. When an F1 female is backcrossed to a triple mutant male, the following 1,000 progeny are produced:

Wild type eyes, wings, and bristles:	90 females, 89 males
Wild type eyes and bristles, vestigial:	83 females, 98 males
Wild type eyes and wings, spineless:	37 females, 35 males
Wild type wings and bristles, blue eyes:	36 females, 34 males
Wild type wings, blue eyes, spineless:	92 females, 88 males
Wild type eyes, spineless, vestigial:	34 females, 39 males
Wild type bristles, vestigial, blue eyes:	33 females, 37 males
Blue eyes, spineless, vestigial:	90 females, 85 males

Calculate the map distance between blue eye and any linked genes. Show your work.

BIOL10005 Lecture Notes - Lecture 6: Karyotype, Color Blindness, Y Chromosome

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