Human Genetics Flashcards
Distinguish between:
1. Genes and alleles
2. Characters and traits
3. Genotype and phenotype
4. Chromatin, chromosome, and chromatid 5. Haploid and diploid cells
a) A gene is a unit of heredity which controls a particular character.
b) An allele is a specific form of a gene which controls a trait. For example, a specific
allele for a hair colour gene may determine that an individual will have the trait brown hair. The gene controls hair colour, whereas the allele determines that the hair colour will be brown. Note that individuals carry pairs of alleles, one on each of two chromosomes of any pair for any particular characteristic being controlled.
c) A character is any observable condition or feature which can exist in various forms. For example, eye colour and hair colour are characters.
d) A trait is a specific form of a character. For example, brown eye colour and black hair colour are traits.
e) Genotype is a description of the genetic makeup of the individual. For example, saying that someone carries a dominant and a recessive allele for hair colour is a description of the individual’s genotype. Genotypes may be described using words or symbols such as Aa. In this example A refers to a dominant allele and a refers to a recessive allele. Aa implies that the individual carries both a dominant and a recessive allele.
f) Phenotype is the term used when to describe the traits displayed by an individual. Saying that someone has blue eyes is a description of the person’s phenotype.
g) Chromatin is a complex of DNA and protein that functions to package very long
DNA molecules into more compact structures called chromosomes.
h) Chromatids two thread like strands which make up a replicated chromosome during
cell division. Each chromatid contains one strand of a double helix of DNA.
i) Chromosome are long strands of DNA found in the nuclei of cells. Genes located on chromosomes. Thousands of genes are located end-to-end on each of these DNA strands. They are passed from the parents to the child and control all cellular activity.
j) Haploid refers to a cell which has a single set of unpaired chromosomes. A human egg cell for example has one of each of the 23 different chromosomes that are present in human cells.
k) Diploid refers to a cell which has two of each chromosome. A fertilized human egg would have a haploid set of chromosomes (23) from the unfertilized egg and another haploid set of chromosomes from the sperm cell (23). The fertilized egg (diploid) would have 23 pairs of chromosomes.
Know the difference between the karyotypes of a normal human female and a normal human male.
Diploid human cells each have 46 chromosomes (23 pairs). Half (23) of these chromosomes are inherited from the mother, and the other half are inherited from the father.
Sex chromosomes are similar to autosomal chromosomes, but are related to the development of sex in humans. Humans have 22 pairs of autosomal chromosomes, and 1 pair of sex chromosomes; in females, both chromosomes in this pair are X- chromosomes, whereas males have 1 X and 1 Y chromosome
Draw a diagram showing the characteristics and appearance of cells during each stage of mitosis and meiosis.
Define the term nondisjunction.
Nondisjunction refers to the failure of paired chromosomes to separate during the first
meiotic division of for sister chromatids (the two chromatids of one chromosome) to
separate normally during the second meiotic cell division. Nondisjunction could result in an abnormal distribution of chromosomes in the daughter cells. Daughter cells could
have extra or missing chromosomes.
Identify the two processes that occur during meiosis that generate genetic variability between gametes (crossing over and independent assortment) during meiosis.
During Meiosis I, parts of non-sister chromatids may be exchanged through a process named crossing over; this process results in new genetic combinations
During Meiosis I, paternal and maternal chromosome pairs align randomly along the metaphase plate; this may result in alternative chromosome arrangements which then sort independently into daughter cells (independent assortment).
Both crossing over and random alignment result in gametes that are genetically different from one another as well as the parent cell that produced them – in other words, genetic variation.
istinguish between:
1. Homozygous and heterozygous genotypes
2. Dominant and recessive alleles
3. Autosomal and sex-linked inheritance
