Topic 6 - Inheritance, variation and evolution Flashcards
What is DNA
The chemical that all the genetic material in a cell is made up from. A double stranded polymer of nucluotides, wound to form a double helix.
What are chromosomes and what is their function
Coiled up lengths of DNA that determine the characteristics you have
What is the Shape of DNA
Double helix
What is a gene
A small section of DNA found on a chromosome that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
What does each gene do
Code for a particular sequence of amino acids
How many amino acids are there
20
What determines what proteins the cells produce
DNA
What is a genome
The entire genetic material of an organism
Reasons understanding the human genome is important (3)
Scientists can identify which genes are linked to different diseases- Knowing which genes are linked to inherited diseases could help us understand them better and how to treat them - Trace immigration
What is sexual reproduction
Type of reproduction that involves the production of gametes with meiosis. gametes from each parent fuse to form zygotes
What are gametes
Sex cells that are haploids meaning they have half the number of chromosomes
What is meiosis
Cell division that forms gametes in reproductive organs, involving the halving of the chromosomes and 2 divisions
What occurs prior to meiosis
interphase- copies of genetic information are made during this process
What happens in the first stage of meiosis
Chromosome pairs line up at center-Pair of chromosomes separated and move tp opposite poles at random-Membrane splits -Chromosome number halved
What happens in the second stage of meiosis
-Chromosomes line up along centre -Chromatids separated and move to opposite poles -Membrane splits again-4 unique haploid gametes are produced
Why is meiosis important for sexual reproduction (2)
Increases genetic variation -Ensures zygote formed at fertilisation is diploid
Descrtibe fertilisation and its resulting outcome
gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis -As the embryo develops, cells differentiate
What is asexual reproduction
Reproduction that only requires one parent and only involves mitosis
What is a chromosome
A long, coiled molecule of DNA that carries genetic information
How many chromosomes do human body cells have
46 (23 pairs)
How many chromosomes do human gametes have
23
What is a nucleotide
A monomer of DNA
What are nucleotides made of
Sugar -Phospate -(Nitrogenous) Base
What is a gene
Small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
What are monomers of DNA
Nucleotides
What are alleles
Different versions of the same gene
What is a dominant allele
A version of a gene where only one copy is needed for it to be expressed
What is a recessive allele
a version of a gene where two copies are needed for it to be expressed
Wat is meant when an organism is homozygous
When an organism has two copies of the same allele (two recessive or two dominant)
What is meant when an organism is heterozygous
When a organism has two different versions of the same gene (one recessive or one dominant)
What is the genotype
The alleles present for a particular gene
What is a phenotype
The visible characteristic
How are dominant alleles represented in a punnett square
Uppercase letters
How are recessive alleles represented in a punnett square
lowercase version of same leter as dominant allele
Draw a punnet square for a cross between a homozygous recessive blue eyed female (bb) with a heterozygous brown eyed male (Bb)
:
Draw a punnet square for a cross between a homozygous dominant blue red flower (RR) with a homozygous recessive white flower (rr)
:
Draw a punnett square for a cross between two heterozygous custic fibrosis carriers (Ff)
:
PKU is a recessive condition. Two heterozygous parents (Pp) have offspring, predict the proportion of offspring that will have PKU (draw punnets square)
75% chance of having normal phenotype and 25% chance of PKU phenotype
what is the problem with single gene crosses
Most characteristics are controlled by multiple alleles rather than just one
What is an inherited disorder
A disorder that?s caused by the inheritance of certain alleles
2 examples of inherited diseases and what gene they are caused by
Cystic fibrosis (caused by a recessive allele), polydactyl (caused by dominant allele)
How embryos screened for inherited diseases
during IVF, one cell is removed from 8 cell embryo and tested for allele caused disorders. If cellhas no indicator alleles, then embryo is implanted into uterus
3 ethical issues with embryo screening
Could lead to beliefs of inferiority of disabled people or people with disorders, destruction of embryos with inherited disorders seen as murder by some people, Could be views as part of designer baby concept
what is gene therapy
Insertion of normal allele into cells of person with inherited disorder to functionally replace the faulty allele
Ethical issues of gene therapy (2)
Some believe that it is going againt god, Introduced genes could enter sex cells and be passed to future generations
What are sex chromosomes and which do males and females have
Pair of chromosomes that determine sex: males= XY females=XX
economic issue concerning embryo screening
Costs of hospital tretment and medicationj will need to be considered if it is known that a child will have an inherited disorder and financial support explored if necessary (insurance)
Social positive of embryo screening
if embryo terminated, future suffering is prevented
what is a species
A group of organisms with similar characteristics which are able to interbreed to produce fertile offspring
4 different bases
A,C,G,T
Which bases are complementery
A,T and G,C
Describe how nucleotides interact to form a molecule of DNA
- Sugar and phosphate molecules join to form a sugar phosphate backbone in each DNA strand
- Base connected to each sugar
- Complementary base pairs joined by weak hydrogen bonds
How does a gene code for a protein
- A sequence of three bases in a gene forms a triplet
- Each triplet codes for an amino acid
- The order of amino acids determines the structure and function of protein formed
Why is the folding of amino acids important in proteins
It folds into a unique shape that enables the protein to do their job as enzymes, hormones or forming structures like collagen
2 stages of proteinj synthesis
transcription and translation
What happens in transcription
The formation of mRNA form a DNA template
Outline transcription (4) or simple
- DNA double helix unwinds
2.RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand - RNA polymerase joins free RNA nucleotides to complementery bases of the coding DNA strand
4.mRNA formation is complete and the mRNA detatches and leaves the nucleus
simple: - DNA double helix unwinds
- Base sequence of gene is copied into complementary mRNA
This leaves the nucleus
What happens in translation
A ribosome joins amino acids in a specific order dictated by mRNA to form a protein
Outline translation (4)
- mRNA attatches to a ribosome
- Ribosome reads mRNA bases in triplets.
- Each triplet codes for one amino acid, so amino acids brought to the ribosome by a tRNA molecule
- ribosome reads triplets of bases on mRNA and causes it to join amino acids in correct order, then it fold into shape
What does a base triplet do
Code for one amino acid
Importance of understanding human genome (3)
Search for genes linked to different types of diseases
understanding and treating inherited disorders
tracing human migration patterns from the past
What is a mutation
A random change in the base sequence of DNA which results mostly in no change to the protein coded for, or genetic variants of protein (slight alteration but appearance and function remain)
Occur continuously
Describe the effect of a gene mutation in coding DNA
- If mutation changes the amino acid sequence, protein structure and function may change
- If mutation does not change amino acid sequence, there is no effect on protein structure/function
Effect of gene mutation in coding DNA for enzyme
Enzyme shape may change so active site doesn’t fit substrate and structural proteins may lose their strength
What is non-coding DNA
DNA which doesn’t code for a protein but instead controls gene expresion
Effect of gene mutation on non-coding DNA
Gene expression may be altered, affecting protein protein and the phenotype
