AP Biology Beyond Mendel’s Laws of Inheritance

AP Biology Sex linked traits  Genes are on sex chromosomes  as opposed to autosomal chromosomes  first discovered by T.H. Morgan at Columbia U.  Drosophila breeding  good genetic subject  prolific  2 week generations  4 pairs of chromosomes  XX=female, XY=male 1910 | 1933

AP Biology Huh! Sex matters?! F 2 generation 100% red-eye female 50% red-eye male 50% white eye male Discovery of sex linkage P X F 1 generation (hybrids) 100% red eye offspring true-breeding white-eye male true-breeding red-eye female

AP Biology  In humans & other mammals, there are 2 sex chromosomes: X & Y  2 X chromosomes  develop as a female: XX  gene redundancy, like autosomal chromosomes  an X & Y chromosome  develop as a male: XY  no redundancy Genetics of Sex XY X X XX XY 50% female : 50% male XX

AP Biology XRXRXRXR XrYXrY Morgan’s flies… x XrXr Y XRXR 100% red eyes XRXR XRXrXRXr XRYXRY XRYXRYXRXrXRXr x XRXrXRXr XRYXRY XRXR Y XRXR XrXr XRXrXRXr XRYXRYXRXRXRXR XrYXrY 100% red females 50% red males; 50% white males

AP Biology Genes on sex chromosomes  Y chromosome  few genes other than SRY  sex-determining region  master regulator for maleness  turns on genes for production of male hormones  X chromosome  traits other than sex determination  mutations: (all are recessive)  hemophilia  Duchenne muscular dystrophy  color-blindness

AP Biology Hemophilia Hh x HH XHYXHY XHXhXHXh XHXhXHXh XHXH XhXh XHYXHY Y XHXH sex-linked recessive XHXH Y male / sperm XHXH XhXh female / eggs XHXHXHXH XHXhXHXh XHYXHYXhYXhY XHXHXHXH XHYXHY XHXhXHXh XhYXhY carrierdisease

AP Biology Sex-linked disorders  Most sex-linked disorders are found on the X chromosome.  Boys are more affected than girls.  Duchenne muscular dystrophy  Hemophlia  Colored blindness

AP Biology X-inactivation  Female mammals inherit 2 X chromosomes  one X becomes inactivated during embryonic development  condenses into compact object = Barr body  which X becomes Barr body is random  patchwork trait = “mosaic” XHXH XhXh XHXhXHXh patches of black patches of orange tricolor cats can only be female

AP Biology Linked Genes  Genes located near each other on the same chromosome tend to be inherited together.

AP Biology Linked genes  Linked genes can be separated by crossing over of homologous chromosomes during prophase I of meiosis.  These offspring are known as recombinants or recombinant types.

AP Biology Mapping the distance between genes  A genetic map based on recombination frequencies is called a linkage map.

AP Biology Errors in Meiosis  Caused by nondisjunction in meiosis I or meiosis II.

AP Biology Errors in Meiosis  Aneuploidy – having an abnormal number of chromosomes  Monosomic – having a missing chromosome  Trisomic – having one extra chromosome.  Polyploidy – having one or more extra sets of chromosomes

AP Biology Alterations of chromosome structure

AP Biology Human disorders due to chromosomal alterations  Down Syndrome (trisomy 21)  Edwards Syndrome (trisomy 18)  Patau Syndrome (Trisomy 13)  XXY – Klinefelter syndrome  XO – Turner Syndrome  XXX – no problems  XYY – no problems  Philadelphia Chromosomes  Cri du chat

AP Biology Genomic Imprinting  Variations in phenotype depending on whether an allele is inherited from the male or female parents.  Happens during gamete formation and silences a particular allele of certain genes.  Angelman Syndrome  Prader-Willi Syndrome

AP Biology Inheritance of organelle genes  Some organelles have small circular DNA. These organelles reproduce themselves and transmit their genes to daughter organelles.  Mitochondria – organism’s inherit their mother’s mitochondrial DNA  Chloroplasts