X-linked traits

Modes of Inheritance Autosomal Inheritance –Dominant vs. Recessive X-linked Inheritance –Genes only on X chromosome –Dominant vs. Recessive Codominance or Incomplete Dominance Cytoplasmic or Maternal Inheritance

Sex Determination Pairs of chromosomes match Sex chromosomes don’t always match –X and Y –Females: X and X chromosome –Males: X and Y chromosome Cannot live without X chromosome –Y chromosome determines males

Females are XX Possible gametes: all eggs will have one X chromosome X X X X X

Males are XY Half of male gametes will have one X chromosome Half of male gametes will have one Y chromosome X Y X X Y Y

Punnett squares predict sex of offspring Genotype: 1XX:1XY phenotype: 1 female:1 male

X-linked traits X is a sex chromosome It also has hundreds of genes –Very few have to do with gender Y does not have many of these genes –Very small chromosome –“sex determining” gene –“male fertility” genes

History of X-linked genes Thomas Hunt University in 1910 –Two students: Alfred Strutevant & Calvin Bridges Found white eye male fly(mutant) Normal(red eyes)

They noted something weird… Mated white eyed male w/ red eyed female(normal) F1 all had red eyes F2 had 3:1 ratio Only males had white eyes Why? x MaleFemale Male

More research Morgan did find a white eyed female Cross with red-eyed female All the male offspring had white eyes!!! What was going on?

Explanation Gene for eye color is found on X chromosome –Eye color gene is on different chromosomes in humans Gene not found on Y chromosome –So males only have allele of that gene These genes called X- linked traits or X- linked genes

Color Blindness: X-linked Inheritance B: dominant normal b:recessive color blind allele Father only has one X chromosome to contribute X chromosome to contribute Mom gives all normal genes

All offspring are normal But all females are now carriers –Seem normal, but carry disease allele –Carry the hidden color blind gene –Create a punnett with a carrier as a mother

X-linked Diseases Certain genes linked to diseases “+” means wildtype –Stands for normal gene –Found in “wild” populations “M or m” stands for mutation that causes disease –M= means mutations is dominant over wildtype –M= means mutations is recessive to wildtype M > + > m M > + > m

Examples of X-linked diseases Dominant X-linked disease (X M ) –Rett’s syndrome –Vitamind D resistance Recessive X-linked disease (X m ) –Infantile spasm syndrome –Duchenne Muscular Dystrophy –Hemophilia A and hemophila B –Two types of autistic disorders –Color blindness

Color Blindness Lack to see certain colors well Hard to distinguish them from other colors Red/Green Color Deficiency: most common –99% of color deficiencies Blue/Yellow Deficiency: very rare –Very rare and way to test Seeing only gray is extremely rare In 8-12% of European males 0.5% of females

2 types of cells in eye Rod cells Rod cells –Supersensitive in dim light –Lets you see at night –Doesn’t see in color Cones –Sees in bright light –Distinguishes color One absorbs red, green, and blue

Color Blindness Red and green cones impaired or don’t work at all Can’t see red or green or see it differently than normal Ready to see colors?

Previous Answer:25 What about this one?

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That was a hard one. Normal:5 Color blind may see 2