Chapter 9 Genetics Sex-Linked Genes Pgs Objective: I can use what I learned yesterday about how genes are physically on chromosomes in order to solve sex-linked genetics problems.
Review Gene Linkage If genes are on the same chromosome, will more likely be inherited together If genes are on the same chromosome, will more likely be inherited together –Will see how genes can be “linked” to sex… This accounts for physical stereotypes: This accounts for physical stereotypes: –Most White people tend to have… –Most Black people tend to have… –Most Asian people tend to have… –Most Red-Heads tend to have…
Connecting Genetics with Meiosis ABCDEFABCDEF abcdefabcdef GhJkGhJk ghJKghJK Chromosomes in Mom
Connecting Genetics with Meiosis Sister chromatids are identical Sister chromatids are identical –Doubled to prepare for division ABCDEFABCDEF ABCDEFABCDEF abcdefabcdef abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK
ABCDEFABCDEF ABCDEFABCDEF abcdefabcdef abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK O R ABCDEFABCDEF ABCDEFABCDEF abcdefabcdef abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK Independent Assortment Metaphase I Line-Up
ABCDEFABCDEF ABCDEFABCDEF abcdefabcdef abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK O R ABCDEFABCDEF ABCDEFABCDEF abcdefabcdef abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK BIG A and BIG F still inherited together - Linked on same chromosome! (A and G are NOT linked, because on different chromosomes & independent assortment) What can change this linkage? Crossing Over!!!
Connecting Genetics with Meiosis ABCDEFABCDEF abcdefabcdef GhJkGhJk ghJKghJK Chromosomes in Mom
Connecting Genetics with Meiosis Sister chromatids are identical Sister chromatids are identical –Doubled to prepare for division ABCDEFABCDEF ABCDEFABCDEF abcdefabcdef abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK
Connecting Genetics with Meiosis Sister chromatids are identical Sister chromatids are identical –Doubled to prepare for division ABCDEFABCDEF abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK ABCdefABCdef abcDEFabcDEF
ABCDEFABCDEF abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK O R ABCDEFABCDEF GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK Independent Assortment Metaphase I Line-Up ABCdefABCdef ABCdefABCdef abcDEFabcDEF abcDEFabcDEF abcdefabcdef
ABCDEFABCDEF abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK O R ABCDEFABCDEF abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK ABCdefABCdef abcDEFabcDEF ABCdefABCdef abcDEFabcDEF Crossing over helps break physical stereotypes!
Location of Genes will affect Linkage ABCDEFABCDEF abcdefabcdef GhJkGhJk ghJKghJK Chromosomes in Mom Will alter chances of recombination
Connecting Genetics with Meiosis Sister chromatids are identical Sister chromatids are identical –Doubled to prepare for division ABCDEFABCDEF ABCDEFABCDEF abcdefabcdef abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK
Connecting Genetics with Meiosis Sister chromatids are identical Sister chromatids are identical –Doubled to prepare for division ABCDEFABCDEF abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK ABCdefABCdef abcDEFabcDEF
ABCDEFABCDEF abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK O R ABCDEFABCDEF GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK Independent Assortment Metaphase I Line-Up ABCdefABCdef ABCdefABCdef abcDEFabcDEF abcDEFabcDEF abcdefabcdef
ABCDEFABCDEF GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK O R abcdefabcdef GhJkGhJk GhJkGhJk ghJKghJK ghJKghJK ABCdefABCdef abcDEFabcDEF ABCdefABCdef abcDEFabcDEF BIG A and BIG B still inherited together - Linked on same chromosome with a VERY low chance of recombination (unlikely to cross over due to distance: being closer together) Some physical stereotypes prevail!!! When do Punnett Square (IF never cross over), then do a monohybrid with them connected abcDEFabcDEF ABCdefABCdef
Sex Chromosomes A set of chromosomes that determines (genetic) sex of the offspring A set of chromosomes that determines (genetic) sex of the offspring –Other chrmsmes. = autosomes (determine “body”) Different organisms have different “systems” Different organisms have different “systems” X-O systemZ-W system Diploid/Haploid system X-Y system
Human Sex Chromosomes Women = XXMen = XY Which is more important for survival? X – Why? Which is more important for survival? X – Why? Who determines sex? Men with Y Who determines sex? Men with Y Punnett Squares can be for just 1 gene on chromosome or entire chromosome itself! ABCDEFABCDEF abcdefabcdef Dd d D d d d d D d d d ABCdEFABCdEF abcdefabcdefXYX X X X Y X X X X Y
Inheritance of Sex Chromosomes Can treat sex as its own unique character! Can treat sex as its own unique character! –2 traits: male / female –Gene = entire chromosome (“alleles” = X or Y) Genetics Problem: The gene for eye color (found on autosome #10 in rabbits) is controlled by simple dominance with red eyes dominant over white. Genetics Problem: The gene for eye color (found on autosome #10 in rabbits) is controlled by simple dominance with red eyes dominant over white. –What are the chances that a heterozygous red-eye male and a white-eye female will have red-eye kids? 50% –What are the chances that a heterozygous red-eye male and white-eye female will have a red-eye boy?
heterozygous red-eye male x white-eye female RrXY rrXX RXRYrXrY rXRrXXRrXYrrXXrrXY rX rX rX 2 characters (each with own alleles) Eye Color: Red = White = Sex: Female-ness = Male-ness = Rr XY Because looking at 2 characters at same time… …must do… Genotype Count RrXX = RrXY = rrXX = rrXY = 1111 Phenotype Count Red-eye male = Red-eye female= White-eye male = White-eye female= Chance of having red-eye boy? Chance that a son will have red eyes? 25% 50%
Sex-Linked Traits X chromosome carries genes that are NOT involved in sex determination (still vital to survival) X chromosome carries genes that are NOT involved in sex determination (still vital to survival) –Will be inherited WITH the X chromosome (linked!) –Traits determined by these genes are sex-linked! Y chromosome determines if male why? Y chromosome determines if male why? –Size difference! X bigger than Y carries more genes!
Sex-Linked Traits – Geno./Pheno. Eye color is a sex-linked trait for fruit flies. Red eyes are dominant over white. Eye color is a sex-linked trait for fruit flies. Red eyes are dominant over white. Key: Red = White = Key: Red = White = –Add as superscripts to X chromosome only! Females ( ♀ ) Males ( ♂ ) Red Eyes (Homozygous) X X X Y Red Eyes (Heterozygous) X X X Y White eyes X X X Y Rr RR RR R r rrr Only X chromosome can hold alleles X R Y Red eye male No homozygous or heterozygous
Sex-Linked Traits – Punnett Sq. Cross a female fly that has homozygous red eyes with a white-eyed male fly Cross a female fly that has homozygous red eyes with a white-eyed male fly CROSS: _______x _______ CROSS: _______x _______ ♀ ♂ ♀ ♂ What are the chances of having a red-eyed female? What % of daughters have red eyes? What % of sons will have red eyes? XrXrXrXrY XRXRXRXR XR XrXR XrXR XrXR Xr X R Y XRXRXRXR XR XrXR XrXR XrXR Xr X R X r Y 50% 100%
Sex-Linked Traits – Punnett Sq. Cross a white-eyed female fly with a red-eyed male fly Cross a white-eyed female fly with a red-eyed male fly CROSS: _______x _______ CROSS: _______x _______ ♀ ♂ ♀ ♂ What are the chances of having a red-eyed male? What % of daughters have red eyes? What % of sons will have white eyes? XRXRXRXRY XrXrXrXr XR XrXR XrXR XrXR Xr X r Y XrXrXrXr XR XrXR XrXR XrXR Xr X r X R Y 0% 100%
Sex-Linked Conclusion & Connection to Gene Linkage Explains why sons tend to take after mothers Explains why sons tend to take after mothers –Sons get only Y chromosome from dad –Any traits on X can only come from mother Explains why daughters tend to take after fathers Explains why daughters tend to take after fathers –Fathers can contribute genes on X chromosome –Daughters still get an X from mom, too –Daughters/fathers seems similar when compared to sons/mothers (more relative feel) Sex-Linked truly proved that chromosomes hold genes (X NEVER crosses over with Y) Sex-Linked truly proved that chromosomes hold genes (X NEVER crosses over with Y)