Gene Worksheet

PS 1130A, Human Growth and Development

Chapter 1 worksheet on genes

Match the sentence with the word below.

HUMAN GENETICS

In humans, all cells (except eggs and sperm) contain 46 chromosomes.

This diploid chromosomal number represents two complete (or nearly complete) sets of genetic instructions - one from the egg and the other from the sperm.

At fertilization, the chromosomes for the same traits pair up (homologous chromosomes)

(1)______Allele_____ - genes (Gene - segment of DNA that codes for single protein) coding for the same traits on each pair of homologous chromosomes. The alleles may be identical or different.

(2)____Homozygous__________- when both alleles in a homologous chromosome pair have the same expression. Example: both alleles code for straight hairline at forehead.

(3)______Heterozygous__________- when the alleles differ in their expression. Example: one allele codes for straight hairline and the other for widow's peak.

(4)______Dominant_________- in a heterozygous pair of alleles, it is the one that exerts its effects (is expressed)

(5)_____Recessive__________- the allele with less potency, it is present but its effects are not expressed.

Recessive alleles exert their effects only when homozygous.

(6)______Genotype_________- an individual’s genetic makeup. Whether he/she is homozygous or heterozygous

(7)______Phenotype__________- the manner in which genotype is expressed - Example: the presence of a widow's peak or not, blue vs brown eyes, etc.

Monohybrid - one pair of alleles determine a trait. (Most traits are not determined by a single allele pair, but these will be used as an example).

Use of Punnett Square - a grid used to determine the possible genotypes, and thus resulting phenotypes of offspring. Utilizes the alleles of both parents.

Sex Linked Inheritance

Of the 23 pairs of homologous chromosomes, 22 pairs are referred to as autosomes.

(8)___Autosomes__________ contain genes that determine most body characteristics....