Genetics Flashcards
What is the progression of structures within an organism?
genes => DNA => chromosomes => nucleus => cells => tissues => organs => systems
What are genes and DNA?
Genes are made up of DNA (deoxyribonucleic acid), arranged in a particular patterns
genes code for proteins
genes code in triplets
A binds to T with 2 hydrogen bonds
C binds to G with 3 hydrogen bonds
What is a karyotype?
A genetic ‘picture’ of a diploid cell which has a full complement of chromosomes (23 pairs - 22 autosome pairs and 1 sex chromosome pair)
What are autosomes and sex chromosomes?
autosomes are chromosomes that aren’t sex chromosomes
sex chromosomes are those that determine sex - XX = female, XY = male
fathers determine the sex of the offspring by giving either an X or a Y sex chromosome
What is mitosis?
- normal cellular replication for growth and repair
- 1 nuclear division, 1 cell becomes 1 identical daughter cells
- each daughter cell has a full set of chromosomes
- diploid number = 23 pairs
What is meiosis?
- occurs in reproductive organs
- create ova and sperm
- 2 nuclear divisions
- 1 cell becomes 4 (non-identical)
- each daughter cell has half the number of chromosomes, randomly assigned
- haploid number = 23 chromosomes (not pairs)
At fertilisation, 23 from the ovum + 23 from the sperm = 23 pairs - diploid number restored
What is mitochondrial DNA?
- DNA within our cells’ mitochondria
- 37 pairs
- offspring receives only maternal mitochondrial DNA
What are alleles?
- alleles are matched genes.
- each individual possesses two alleles for each gene
- one allele from the mother and one allele from the father
- allele code for genetic traits such as height, eye colour, the ability to roll the tongue
- if two alleles code for the same trait, they are homozygous
- if two alleles code for different traits, they are heterozygous
Dominant alleles (written in caps) mask recessive alleles (written lower case)
What are genotypes and phenotypes?
- genotypes are the genetic makeup of an organism
- phenotypes are the observable genetic outcome (eg, blue eyes, curly hair, etc)
What is a Punnett square?
- a visual representation of potential offspring genetic variations based on their parents’ dominant and recessive genes
What are autosomal dominant genetic disorders
- disorders where the abnormal allele is dominant
- most people with autosomal dominant genetic disorders are heterozygous, as a homozygous representation would be fatal
What are autosomal recessive genetic disorders?
- disorders where the abnormal allele is recessive
- condition expressed equally in males and female
- generation skipping can occur
- occurs more often with consanguinity (mating in close relatives)
What are sex-linked disorders?
- disorders involving the X or Y chromosome
- most are recessive
- X linked disorders are usually expressed in males, as females have a second X chromosome to mask the abnormal allele
- Y linked disorders are uncommon because the Y chromosome contains relatively few genes
- can only transfer from father to son, only present in males
What are chromosomal disorders?
- disorders relating to the number of chromosomes
- monosomy = one copy of a chromosome - frequently fatal - eg. Turner’s syndrome (female’s with only one X chromosome
- trisomy = three copies of a chromosome
eg trisomy 21 - Down’s syndrome - polysomy = three or more copies of a chromosome
eg Klinefelter’s Syndrome - males with two or three X chromosomes (XXY or XXXY) - results in breasts and infertility - the rate of chromosomal disorders increases with maternal age as ova become less able to precisely split their chromosomes during meiosis
What is genetic testing?
It tests for genetic diseases (structural abnormalities in the DNA) such as Huntington’s diseases.
Huntington’s is a dominant abnormality that doesn’t express until after child-bearing age, and parents have a 50% chance of passing it on to their children.
Also tests for BRCA1 and BRCA2 - breast cancer genes
