Genetics Flashcards
What are chromosomes?
Long molecules of DNA inside a nucleus.
23 pairs inside the nucleus of body cells.
What is DNA?
DeoxyriboNucleic Acid. It is a chemical that all genetic material in a cell is made from. It is a polymer. It is made up of two strands coiled together as a double helix.
What is the structure of DNA?
DNA strands are polymers made up of repeating nucleotides.
Each nucleotide is made up of one sugar (deoxyribose) and a phosphate.
The sugar phosphate molecules form the backbone to the DNA stands. One of the four bases ACTG joins to the sugar molecule.
How do the bases pair in DNA?
A-T and G-C
How many bases code for an amino acid?
Three/triplets
What is a gene?
Small section of DNA found on a chromosome
Genes tell cells in what order/sequence to put amino acids in to make specific protein.
How are proteins synthesised?
DNA unwinds exposing one strand.
An mRNA copy is made using the DNA as a template.
U replaces T.
The first stage happens in the nucleus.
mRNA is single stranded and can leave through the DNA pore.
Proteins are made in the cytoplasm.
The ribosome reads the mRNA . Every three bases codes for an amino acid.
The correct amino acids are brought to the ribosome by carrier molecules. tRNA. This stage is called translation.
What do genes code for?
A particular sequence of AMINO ACIDS put together to make SPECIFIC PROTEINS
What is a genome ?
The entire set of genetic material in an organism
Why is it important to understand the human genome? (3)
1)Allows scientists to IDENTIFY GENES that link to different types of disease i.e Down Syndrome
2)Development of effective treatments
3)Can be used to trace migration of certain populations by tiny differences in GENOMES.
How many chromosomes are in a normal body cell?
46 or 23 pairs
How many chromosomes in a gamete (sex cell)?
23
Give 3 details of sexual reproduction in plants/animals
-Animal gametes -egg & sperm
- Plant gametes-ovule & pollen
-Each gamete contains 23 chromosomes
-nucleus of both gametes fuses=mixture of genetic info=variation in offspring
Give 3 details of Asexual reproduction
-One parent
-Genetically identical offspring-clone
-Happens by mitosis
Give 2 examples of organisms that reproduce asexually
Bacteria
Some animals & plants
What type of cell division are gametes (sex cells) produced by?
Meiosis
What are the 5 stages of Meiosis
1 - Duplicate genetic info-forming ‘X’ chromosomes that arrange themselves into pairs
2 - Chromosomes line up in centre of cell in homologous pairs
3 - Pairs pulled apart so each new cell only has one copy of each chromosome-some of the father’s chromosomes and some of the mother’s go into each cell randomly, but each cell has an equal amount of chromosomes in total
4 - 2nd division-chromosomes line up in centre & separated again
5 - 4 gametes-each with single set of chromosomes
Give 2 details about the 4 gametes produced in meiosis
1 - Each contain 1 set of chromosomes
2-Each gamete genetically different
Why are gametes produced in meiosis genetically different?
Because chromosomes are shuffled up during meiosis and each gamete only gets half of them at random
Explain how/why the cell produced by gamete fusion replicates itself (3)
1) After 2 gametes fused during fertilisation-resulting new cell divides by mitosis to make copy of itself
How many pairs of chromosomes are in a human body cell?
23 Pairs
What do each of the chromosomes control?
22 pairs of chromosomes are matched/homologous pairs-control CHARACTERISTICS
What are the male and female chromosomes?
Males: XY-The Y chromosome causes male characteristics
Explain the chances of a child being male/female using a punnet diagram.
50% chance of male and 50% chance of female.
How do you use genetic diagrams to find the probability of getting a boy or a girl? (3)
1-Put possible gametes from one parent down side, and from other parent along the top
What do the pairs of letters in the middle of a Punnett square show?
The possible gamete combinations
What do inherited genes control?
The characteristics you develop. Genes code for proteins.
What are alleles?
VERSIONS of genes. You have 2 versions (alleles) of every gene in your body-one on each chromosome in a pair
What does it mean if an organism is Homozygous?
If its 2 alleles for a particular gene are the same.
What does it mean if an organism is Heterozygous?
If its 2 alleles for a particular gene are the different.
If two alleles are different (heterozygous), which characteristics will be expressed?
In heterozygous individuals the dominant characteristic will always be expressed/show up in the phenotype/characteristic.
What is a genotype?
The combination of alleles you have e.g- BB Bb etc
What is a phenotype?
Visible characteristics of an organism, due to its genotypes’ interaction with the environment
A person who is heterozygous for brown eyes (Bb) has children with a person who has blue eyes (bb). What percentage of their children will have blue eyes?
50%
How do you interpret a family tree diagram/pedigree diagram?
square-male
What is cystic fibrosis?
It is a genetic disorder of the cell membranes. Causes thick, sticky mucus to build up in air passages and pancreas.
Cause of cystic fibrosis?
Caused by a Recessive Allele -‘f’
What is Polydactyly + cause
A genetic disorder where a baby is born with extra fingers or toes.
Why can’t you have carriers of Polydactyly?
It is caused by a dominant allele. If you get one copy of the allele the phenotype will be expressed.
What is the chance of someone not being born with Polydactyly if both parent are heterozygous (Dd) for the disease.
25%
How can genetic disorders be detected?
EMBRYONIC SCREENING
