Chapter 14

Thomas Hunt Morgan (1933) Used fruit flies (Drosophilia melanogaster) Females had 8 paired chromosomes while males have 3 pairs and 1 mismatched pair

Why use flies? Fruit flies are ideal to use because: 2mm – many can be kept in a small space Rapid life cycle – breed in 4 days 1 pair produces ~ 300 young Short life span – 14 days 8 chroms per body cell

How is sex determined? Sex Chromosomes – mismatched chroms that determine sex In humans, X or Y - Always a 50:50 chance of a boy or a girl with males determining sex of child Humans have 46 chrom/body cell. Last two are sex chroms. 22 autosomes & 2 sex chroms XY XXXYXY XXXYXY

Sex Linkage Morgan noticed that some traits in fruit flies were inherited differently in males than in females. Males seem to inherit certain traits w/ a greater frequency than females. P 1 :Wild type female X White eyed male F 1 :Wild type F 2 :75% Wild type25% White males (All females & ½ (Only males) of the males)

How was the gene for eye color related to being a male? The gene for eye color is carried on the X chromosomes.Conclusion: The gene for eye color is carried on the X chromosomes. The Y chromosome is shorter than the X and has no corresponding gene for eye color.

Human Sex Chromosomes The X chromosome is much larger than the Y chromosome. Genes that are located on the top of the X chromosome are not on the Y chromosome Males either have the trait or are normal Females can be carriers for the traits.

Normal female Carrier female Female w/ trait Normal male Male w/trait

Crosses: Cross a carrier red-eyed female w/ a white eyed male. X R X r x X r Y PR: Cross a red eyed male w/ a carrier red eyed female. X R Y x X R X r

Can a female have white eyes? Cross a Carrier red eyed female with a white eyed male. X R X r x X r Y PR:

Sex-linked traits in humans 1.Red-Green color blindness – recessive. Can’t distinquish between colors 2.Muscular dystrophy- recessive – weakens then destroys muscle tissue 3.Hemophilia – recessive – lacks ability to produce clotting factor – bleeders –Ran rampant through the royal families of Europe – “Royal Hemophilia”

Here is a test for you. Look at the figures below and write down what you see. Do not talk or make any comments during this test!. 4. If you could not see the 29, 45, 56, 6 or 8, you are color blind!! 12 – 20% of the population has this trait. How colorblind people see colors

My colorblind husband and carrier daughters

Sex Linked Problems

Cross a colorblind male with a carrier female

What percent of the boys may have hemophilia if their mother is pure normal and their father is a hemophiliac?

If both parents are normal vision, show the cross that could result in a colorblind son

If 2 parents are normal and nd their son has MD, what must have been the genotypes of the parents?

In humans, the gene for color vision is dominant to the gene for red-green colorblindness. X N X N, X N Y = Normal color vision X N X n = Carrier for colorblindness but normal vision X n X n, X n Y = Colorblind Show the cross between a normal visioned carrier female and a normal male. What is the likelihood of them having a colorblind son? Daughter?

Show the cross between a carrier mother and a colorblind father. What is the probability of them having a son that is colorblind? A daughter?

In humans, the dominant allele for a rare form of rickets (Vitamin D deficiency), is located on the X chromosome. This condition can be successfully treated with Vitamin D therapy. Let “R” = the rickets allele & “r” = the normal allele X R X R, X R Y = Affected female, male X R X r = Affected female X r X r, X r Y = normal female, male A couple goes to a genetic counselor to find out the chances of them having children with rickets. The wife is normal, without any family history while the husband is affected by this disease. Phenotype: ________________________________________ Genotype: ________________________________________

What if the wife were affected (but had a normal father) & the husband was normal? Phenotype: ___________________________________ Genotype: ___________________________________

In cats, the black coat pigment (R) is codominant with the orange coat pigment (O). These two alleles are found only on the X chromosome. X B X B, X B Y = Black coated female, Black male X O X O, X O Y = Orange coated female, Orange male X B X O = Tortoiseshell coat (intermingled black and orange in fur) Notice, only females can have tortoiseshell coats. A female tortoiseshell cat mated with an unknown male cat giving birth to 6 kittens (2 orange females, 1 tortoise female, 1 black male and 2 orange males. What was the genotype and phenotype of the father? Phenotype: ____________________ Genotype: _________

Was it the same male cat from above? The owner of a black female cat wants to know which cat fathered her two tortoiseshell female and 2 black male kittens. Was it the same male cat from above?

Pedigrees - like a flow chart of a family’s genetic history. Traces a family’s genes

Roman numerals show each Generation

This pedigree chart shows inheritance of the gene that causes albinism (autosomal recessive trait). N = Normal pigmentation n = Albino gene

A pedigree chart for the inheritance of achondroplasia (ay-kon-druh-play-zhuh), a form of dwarfism. Dwarfism is a dominant autosomal trait D = Dwarfism d = normal height

Karyotypes Diagrams or photo of how chromosomes are arranged and which ones are present from an individual. Chromosome smear KaryotypesKaryotypes can be used to determine abnormalities in chromosome makeup.

A Normal female

A Normal Male

Amniocentesis Method of extracting amniotic fluid w/ fetal cells. Can give sex of child and also a karyotype is produced.

Mutations – aka: what can go wrong. Changes in the genetic material of a cell Types: Gene mutation – affects gametes therefore inheritable – Point & frameshift Chromosomal mutationsChromosomal mutations – involves segments, whole chroms or an entire set of chroms Somatic mutations – affect body cells. Not inheritable. Cancers (skin, etc)

Nondisjuction Involves a whole chromosome or an entire set of chromosomes that fail to separate during meiosis. Gametes may contain extra chromosomes (or missing chromosomes) Another animation

If Sex chromosomes fail to separate properly a. Turner’s Syndrome - 45 XO#1280 Sterile, underdeveloped, short, webbed neck, low hairline May have learning problems 1/2500 births b. Klinefelter’s syndrome – 47 XXY#1281 Underdeveloped, sterile, female characteristics but is a male. 1/1000 births 45YO – Dead – need an X chromosome to survive 47XXX – Triple female – normal mental capacity. Tend to be lighter than normal. Very passive. Are fertile. 1/ XYY – Triple males. 1/1000. Very physical. Fertile. Tends to be more aggressive. 2% of convicts of violent crimes

46XX 45X0 47XXY 46XY Descriptions

If Autosomes fail to separate Trisomy 21Trisomy 21 (or other type of trisomy) – aka; Down’s syndrome Extra #21 chromosome Mild to serious mental deficiency 1/800 births

Down’s Syndrome or Trisomy 21

Extra #21 chromosome

Klinefelter’s syndrome 47XXY

Turner’s Syndrome - 45XO

Polyploidy Entire set or sets of chromosomes fail to separate Fatal in animals In plants, leads to larger, hardier plants 3N, 4N

Polyploidy An entire set of chromosomes fails to separate. Fatal in animals In plants, leads to larger, hardier plants 3N, 4N…

Chromosomal mutations Deletions – loss of a part of a chromosome#1178 Additions – gain of a part of a chromosome (duplication) Inversions – Part of a chrom becomes oriented in the reverse of its normal direction Translocation - crossing over of nonhomologous chroms