April 27, 2010 What is a karyotype? When looking at a karyotype, how can you tell if a child will be normal?

Sometimes chromosomes don’t separate correctly in meiosis In meiosis II, sister chromatids are supposed to move to separate sides of the cell. In some cases, both chromatids go to the same side Gametes end up with two copies of the same chromosome. Called nondisjunction Cause of different genetic disorders such as Down’s Syndrome Trisomy 21 (three copies of chromosome 21)

How is it determined which trait will show up? Each chromosome has a partner (homologous chromosome) with the same genes One from mom, one from dad For example: mom might have blue eyes and dad brown. The child carries one copy of each color, so how is their eye color determined?

VOCAB Allele: version of a gene Ex. Alleles for eye color can be blue, brown, green, etc. All are eye colors, but different versions

VOCAB Dominant Allele: only need one copy to show up Ex. Mom gives allele for blue eyes, dad gives allele for brown eyes. Brown is dominant to blue. Kid will have brown eyes (Bb) Mom contributes the ‘b’ allele, dad contributes the ‘B’ allele. Dad’s allele is dominant to mom’s so it wins! Written as CAPITAL letter

Recessive Allele: need two copies in order to show up Ex. Mom gives allele for blue eyes (b) and dad gives allele for blue eyes (b). Kid will have blue eyes (bb) Written as a lowercase letter

Genotype: genetics of trait (what alleles?) Homozygous: two copies of the same allele Homozygous dominant (BB) Homozygous recessive (bb) Heterozygous: one dominant, one recessive allele Bb

Phenotype: physical characteristic (what you SEE) Genotype of BB gives a phenotype of brown eyes Genotype of bb gives a phenotype of blue eyes Genotype Bb gives phenotype of brown eyes

How can you predict what trait a child will have? Punnett Square