P2- Topic 6- Inheritance, Variation and Evoloution 2022 Flashcards
What is sexual reproduction? 3
Type of reproduction
the joining of male and female gametes, each containing genetic information from the mother or father.
Sperm and egg cells in animals
Pollen and egg cells in flowering plants
What are gametes?2
Sex cells (sperm cells and egg cells in
animals, pollen and egg cells in flowering
plants).
● Haploid (half the number of chromosomes)
what does meiosis lead to 3
formation of four non-identical cells from one cell
Chromosome number is halved.
Involves two divisions
What is asexual reproduction?
Involves mitosis only.
Produces genetically identical offspring
known as daughter cells.
what happens in meiosis 4
a cell divides to form gametes
copies genetic information
cell divides 2x to form four gametes, each with a single set of
chromosomes
all gametes are genetically different from each other.
Why is meiosis important for sexual
reproduction? (2)
increases genetic variation.
ensures the zygote formed at fertilisation is diploid
Describe fertilisation and its resulting
outcome 2
Gametes join together to restore the normal
number of chromosomes and the new cell then
divides by mitosis (which increases the number
of cells).
As the embryo develops, cells differentiate.
Why is understanding the human genome
important?4
The whole human genome has been studied and is
important for the development of medicine in the future
search for genes linked to different types of disease
- understanding and treatment of inherited disorders
- use in tracing human migration patterns from the past
Define genome
The entire genetic material of an organism.
Describe the structure of DNA4
- polymer
- made up of two strands
- forming a double
helix. - DNA contained in structures called chromosomes
What are DNA nucleotides made up of?3
common sugar
phosphate group
one of four different bases attached to the sugar. A,T,C,G
Define gene
-a small section of DNA on a chromosome.
Each gene codes
for a particular sequence of amino acids, to make a specific protein.
what are the monomers of DNA?
Nucleotides
Describe how nucleotides interact to form a molecule of DNA (3)
Sugar and phosphate molecules join to form a
sugar-phosphate backbone in each DNA strand.
Base connected to each sugar.
Complementary base pairs (A pairs with T, C pairs with G)
joined by weak hydrogen bonds
Explain how a gene codes for a protein 3
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
(i.e. how it will fold) and function of protein formed
What is protein synthesis?
The formation of a protein from a gene
What are the two stages of protein synthesis?
- Transcription
2. Translation
What does transcription involve?
The formation of mRNA from a DNA
template
Outline transcription 4
- DNA cannot move out of
the nucleus as it is too big. - The two strands pull apart from each other, and mRNA nucleotides
match to their
complementary base on the strand. - mRNA nucleotides joined together, creating a new
strand called the mRNA strand. This is a template of the original DNA. - The mRNA then moves out of the nucleus to the cytoplasm and onto
structures called ribosomes.
outline translation 4
- mRNA attaches to a ribosome.
- Ribosome reads the mRNA bases in triplets. Each triplet codes
for one amino acid which is brought to the ribosome by a tRNA molecule (carrier molecule). - A polypeptide chain is formed from the sequence of amino
acids which join together
What is a mutation? 2
A random change in the base sequence of DNA
results in no change to the protein coded for, or
genetic variants of the protein (slight alteration but
appearance and function remain)
Describe the effect of a gene mutation in coding DNA 2
the protein structure and function may change (an enzyme may no longer
fit its substrate binding site or a structural protein may lose its
strength).
● If a mutation does not change amino acid sequence, there is no effect on protein structure or function
What is non-coding DNA?
DNA which does not code for a protein but controls which genes are expressed
Describe the effect of a gene mutation in non-coding DNA (2)
Gene expression may be altered, affecting protein production and the resulting phenotype (physical charecteristics)
What are alleles?
Different versions of the same gene
what is a recessive or dominant allele 2
d-A version of a gene where only one copy is needed for it to be expressed
r-A version of a gene where two copies are needed for it to be expressed
what does it mean for a organism to be homozygous or heterozygous 2
homo-When an organism has two copies of the same allele (two recessive or two
dominant)
hete-When an organism has two different versions of the same gene (one dominant and one recessive).
what is a genetype and example
The genes present for a trait
The combination of alleles an individual has, e.g. Aa
What is the phenotype? and example 2
The visible characteristic eye colour
What is the problem with single gene crosses?
Most characteristics are controlled by multiple alleles rather than just one.
Give 2 examples of inherited disorders and allele cause4
Polydactyly (having extra fingers or toes)
dominant allele.
Cystic fibrosis (a disorder of cell membranes
recessive allele.
