Chromosomes and Inheritance

Autosomes vs. sex chromosomes Autosomes = the pairs of chromosomes that are the same in males and females In humans, these are chromosomes # 1 - # 22

sex chromosomes = differ between males and females of a species: differ physically and in the genes they carry In humans, chromosome # 23

sex determination in humans: female gives: male gives: xx & x y & xx female xy male

Alleles alleles are different forms of a given gene ex. gene = tongue rolling tongue roller vs. non-roller

chromosome # 14 tongue rolling gene from mom tongue rolling gene from dad the alleles from mom and dad may be the same, may be different

Genotype = the gene forms, or alleles someone carries Each person carries 2 copies of each gene (on their autosomes)

RR- if they carry the same allele on both chromosomes -> HOMOZYGOUS Rr- if they carry different alleles -> HETEROZYGOUS Genotypes

Phenotype = the physical or physiological expression of those alleles

alleles can have different relationships to each other dominant --- recessive 1. a dominant allele, when found in the heterozygous condition, overrides the recessive allele Rr -> will result in a tongue roller

RR = homozygous dominant Rr = heterozygous rr = homozygous recessive GENOTYPEPHENOTYPE roller non-roller

2. incomplete dominance

3. multiple alleles with codominance ex. blood type

Genetic Disorders 1. genetic abnormality- an uncommon version of a trait ex. a person born with 6 fingers

2. genetic disorder- an inherited condition that will result in mild to severe health problems. ex. cystic fibrosis

3. syndrome- a set of symptoms that characterize a given disorder

Autosomal dominant inheritance = trait will typically appear in every generation HH or Hh Ex. Huntington’s disorder (nervous system)- typically fatal in 40’s or 50’s Why does gene stay in population? its effects occur post-reproduction

Autosomal recessive inheritance- trait (disorder) shows up less often in the population because the trait can be masked by the dominant allele Ex. galactosemia: gg lactose galactose glucose-1-phosphate glucose results in a buildup of galactose in blood… damage to eyes, liver, brain X

x-linked recessive traits- gene is only found on the x chromosome- not the Y! malefemale xAxAxAxaxaxaxAxAxAxaxaxa xAyxayxAyxay 33.3%50%

I-1 = King George III III-1 and III-2 = Prince Albert and Queen Victoria IV-5 and IV-6 = Alice of Hesse and Ludwig IV of Hesse V-13 and V-14 = Alix and Nicholas II (Tsar of Russia)Alix and Nicholas II VI-16 = Alexei VIII-1 = Prince Charles Hemophilia in Royal Families in Europe

Changes in Chromosome Number aneuploidy= the condition of having less than or more than the normal diploid number of chromosomes polyploidy- condition of having 3 or more entire sets of chromosomes (lethal in humans)

Down syndromeDown syndrome (trisomy 21): The result of an extra copy of chromosome 21. Down syndrome affects 1:700 children and alters the child's phenotype either moderately or severely.

cause of aneuploidy = NONDISJUNCTION Failure of paired chromosomes to disjoin (separate) during cell division so that both chromosomes go to one daughter cell and none to the other.

Patau syndrome (trisomy 13)Patau syndrome (trisomy 13): serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months.