cytogenetics and sex determination

what is cytogenetics

The study of chromosomes

aneuploidy

number of chromosomes is altered

• One or more chromosomes are added or deleted

polyploidy

one or more complete sets of chromosomes is added

• Organism will be at least 3n

monosomy

loss of single chromosome (2n-1)

trisomy

gain of a single chromosome (2n +1)

what are some duplication errors

1. tandem

2. displaced

3. reverse

tandem duplication

duplicated region is adjacent to the original

displaced duplication

duplicated region is at a distance from the original

reverse duplication

duplicated region has been inverted

deletion

segment of a chromosome is deleted

inversion

segment of a chromosome is inverted

translocation

segment of a chromosome moves from one chromosome to another location on the same chromosome OR to a non-homologous chromosome

Why are cattle more susceptible to Robertsonian translocations?

all their autosomes are acrocentric

how does a Robertsonian translocation occur

when two acrocentric chromosomes fuse at or near their centromeres, forming one larger chromosome

• This causes reproductive problems

why does Robertsonian translocation result in decreased fertility in cattle

Since chromosomes 1 and 29 fuse, gametes will have unbalanced chromosomes at the end of meiosis

why are mules generally infertile

• mules have 63 chromosomes, odd. number

• separation of chromosomes during meiosis is not even, one gamete will end up with too many or too few chromosomes

• horse and donkey chromosomes dont contain the same gene sequences and cant cross over, therefore cannot communicate with each other

what does it mean that early gonads are bipotent

have the ability to differentiate into either male or female structures

how does SRY effect the bipotential gonad

from the Y chromosome, stimulates development of the gonads into testes

• without this protein, the embryo will develop into a female.

What hormone is secreted by Sertoli cells

secrete anti-Mullerian hormone (AMH)

what does anti-Mulleian hormone (AMH) do

degrades Mullerian ducts, which are the precursor to ovarian tubes and uterus

What hormone is secreted by Leydig cells

testosterone

what does testosterone do

causes the differentiation of Wolffian ducts into epididymis, ductus deferens, and seminal vesicle

• Testosterone also causes development of male external genitalia (penis, prostate)

what does the gonad develop without SRY, testosterone and AMH

the ovary, uterine tube, uterus, and internal portion of vagina

What hormone is secreted by granulosa and theca cells

estrogen

what does estrogen do

influences development of female external genitalia

what is Freemartins

shared blood circulation between twins

how does Freemartins develop

• develops from the transfer of bone marrow precursor cells between male twin and female twin → blood chimerism in both calves

• Male twin produces AMH, testosterone and SRY, which enters shared circulation inhibiting the female twins reproductive tract

result of Freemartins

• Both twins will have some blood cells that are 60,XX and some that are 60,XY

• Females are born with underdeveloped genitalia, short blind-ended vagina, and rudimentary ovaries

What is a Barr body, and why is it necessary?

an inactivated X chromosome

• These are necessary because if we have two active X chromosomes, we get double the amount of hormone and proteins

what determines sex of the embryo

the sperm cells Y-chromosome

what is the defult sex

female

mode of inheritance of tortoiseshell cat

sex-linked trait on the X chromosome

• almost exclusively male

sex chromosomes are present in an animal with Trisomy X

XXX

sex chromosomes are present in an animal with Turner Syndrome

XO

sex chromosomes are present in an animal with Klinefelter syndrome

XXY

physical changes are seen in animals with Turner syndrome

• Phenotypically female

• Small stature, poor condition, hard to gain weight

• Gonadal dysgenesis (small ovaries, flaccid cervix, anestrus)

• Angular limb deformities

What physical changes are seen in animals with Klinefelter syndrome?

• Phenotypically male due to Y chromosome

• Infertile because 2 X chromosomes impair spermagogenesis

• Underdeveloped penis and testes

• Lack secondary sexual characteristic

• Maintain juvenile appearance

what is the centromere critical for

proper segregation of chromosomes during anaphase

centromere position possibilities

• telocentric

• acrocentric

• submetacentric

• metacentric

nullisomy

loss of both homologous chromosomes (2n-2)

tetrasomy

gain of 2 homologous chromosomes (2n+2)

species

a group if individuals actually or potentially capable or reproducing with each other with fertile offspring

inbreeding depression

lack of fitness dur to breeding among consanguinous individuals

outbreeding depression

lack of fitness due to breeding among individuals of two very different backgrounds