Genetics Flashcards
What is a gene?
heritable factor that consists of a sequence of DNA and influences a specific trait.
What is the position of gene in the chromosome called?
locus
What are alleles?
Alternate forms of a gene that codes for different variations of a specific trait
State the definition of genome
The totality of the genetic information in an organism. It includes all genes and non-coding sequences.
- human cells have 46 chromosomes
What is a gene mutation?
Change in the base sequence of a section of DNA coding for particular characteristic.
What are the two types of gene mutations?
- somatic
- germline
What are the two types of point mutations?
- substitutions (silent, missense or nonsense)
- frameshifts (insertions and deletions)
Somatic mutation
Occurs in the body cell and affects a tissues
Germline
Occurs in a gamete and affects offspring
Silent mutations
Does not affect the amino acid sequence.
Missense mutations
Affects the sequences and changes the code. It produces a different amino acid at a certain position.
Nonsense mutations
Changes in the sequence that results in giving a rise to a stop codon -> uncompleted protein.
What is the sickle cell anemia?
Sickness that affects the shape of red blood cells, which carry oxygen to all parts of the body (autosomal codominant).
Cause of the sickle cell anemia
- base substitution GAG -> GUG (hemoglobin beta)
- amino acid change Glutamic Acid -> Valine
Consequences of sickle cell anemia
- alters hemoglobin structure
- cannot transport oxygen efficiently
- sickle cells are destroyed at higher rate
What is the heterozygous advantage of sickle cell anemia?
It is a codominant trait and heterozygous individuals demonstrate an increased resistance to malaria.
What are the point mutations?
- substitution of a base (ATG-ACG)
- insertion of a base (ATG- ATCG)
- deletion of a base (ATG-AG)
Gene mutations can be…
- beneficial
- detrimental
- neutral
What is the beneficial gene mutation?
Change in the sequence to create new variations of the trait
What is the detrimental gene mutation?
It cuts of the piece of gene sequence and disrupts the normal function of the trait.
What is the neutral gene mutation?
has no effects on functioning of the specific elements
What are the two ways in which fetal cells can be obtained?
- amniocentesis
- chorionic villus sampling
Explain chorionic villus sampling
cells are sampled from the placenta, specifically the chorion. It can be done earlier than the amniocentesis and the sampling tool enter through the vagina.
- conduced to 11 weeks with a higher risk of miscarriage
Explain the amniocentesis
Involves passing a needle through the mothers abdominal wall. The needle is used to withdraw a sample of amniotic fluid of a developing fetus. Later those cells are used to prepare a karyotype.
- conducted to 16 weeks with a slight risk of miscarriage
What was John Cairn technique?
He pioneered a technique for measuring the length of DNA molecules while uncoiled.
What are diploid cells ?
Sexually reproducing organisms receive genetic material from both parents. They contain 2 sets of chromosomes.
What are haploid cells?
These organisms pass only half of their genetic material. They are haploid and have only one set of chromosomes.
What are homologus chromosomes?
Paired chromosomes that have the same genes at identical loci positions.
What are autosomes?
An autosome is any chromosome that is not a sex chromosome. 22 pairs are homologous autosomes
- each pair has identical genes and loci
- alleles may differ
What are sex chromosomes?
Chromosome concerned in determining the sex of an organism. 23rd pair are the sex chromosomes
- females have two X chromosomes
- males have X and Y chromosome
What is Y chromosome responsible for?
Development of the male characteristics
What are karyotypes?
They identify the number and types of chromosomes in a cell.
Purpose of karyotyping
Identifying sex of the offspring and diagnosing potential abnormalities.
What is the karyogram?
Shows the chromosomes of a cell in homologous pairs of decreasing length.
What are two laws of Mendelian genetics?
- segregation
- independent assortment
Explain the law of Segregation
Separation of alleles. There is a 50% chance that we are going to get either of those genes.
Explain the Independent Assortment
It means that traits do not affect each other because they are not in the same chromosome.
What is cystic fibrosis?
Disorder that damages lungs, digestive tract and other organs. It is inherited from generations (autosomal recessive).
- gene called CFTR on chromosome 7, produces mucus
- people with this disorder produce abnormal number of it because they inherited two copies of CFTR
What is the Huntington disease?
Inherited disorder that results in break down and death of nerve cells. This disease is an autosomal dominant disorder
- mutation in HIT gene that codes for huntingtin
Color blindness
Parents pass down the genes for red-green color vision deficiency through the X chromosome.
- X linked recessive inheritance
Chromosomal mutation
Involves long segments of DNA.
- deletions, insertions, inversions or translations of segments of DNA
Examples of the chromosomal mutations
- down syndrome (translocation)
- Turner syndrome (deletion)
Down syndrome
Genetic disorder caused by abnormal cell division that results in extra copy of the 21 chromosome.
Hemophilia
Inherited bleeding disorder in which blood does not clot properly, because it does not have enough blood clotting proteins.
- located on X chromosome
What is the Turner Syndrome?
Condition that affects only females. Results when X chromosome is missing. The error happens during the formation of egg or sperm. It contributes to short height and heart diseases.
Polygene
group of genes that produce a specific phenotype or a trait.
Locus
position on homologous chromosomes of a gene
What is meiosis?
Reduction division of a diploid cell to produce four haploid cells (gametes).
What are the two divisions of meiosis?
- meiosis I that separates homologous chromosomes
- meiosis II that separates sister chromatids
What is the crossing over?
The exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.
- occurs via synapsis in prophase I
Chiasmata
represent the points where genetic information has been exchanged between the homologous pair
State the definition of recombinants
non-sister chromatids that have exchanged DNA