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.
The 23rd pair, the sex chromosomes determine the sex of an individual that is whether an individual will be male or female.
Females possess two sex chromosomes that look alike, the (9) _____x chromosomes_____________.
Males possess two dissimilar sex chromosomes, referred to as X and Y.
Possession of the (10) _____y chromosomes____________determines maleness. The Y sex chromosome is only about a third the size of the X sex chromosome and it lacks many of the genes (directing characteristics other than sex) that are found on the X.
(11)_________sex linked___________ - genes present only on the X sex chromosome. Include those that determine normal color vision and conversely color blindness, normal clotting ability and conversely hemophilia. The alleles that determine color blindness and hemophilia are recessive. In females both X chromosomes must carry the recessive alleles for a woman to express either of these conditions. (Thus occur infrequently). In males, even one sex linked recessive allele will exhibit the recessive phenotype because his Y chromosome lacks any genes that might dominate or mask the recessive allele.
Males always inherit sex-linked conditions from their mothers (on the X chromosome).
Males cannot inherit sex-linked conditions from their fathers because they receive the Y chromosome from the father. (XY determines male offspring).
Word pairs:
Sex linked genes
Recessive gene
Genotype
Y chromosome
Homozygous
Alleles
Heterozygous
Phenotype
Autosomes
X chromosomes
Dominant