B5.1 - Inheritance Flashcards
Phenotype
Appearance of an organism
Variation
Differences within a species
Two type/causes of variation:
- genetic variation (genetic material inherited from parents)
- environmental variation (environment in which you live in)
Characteristics causes by genetic variation:
- eye colour
- blood group
- genetic disorders
(Caused by genes)
Characteristics caused by environmental & genetic variation
- height
- weight
Characteristics caused by environmental variation
- intelligence
- language spoken
- good swimmer
Discontinuous variation
- characteristics fall into distinct groups
- genetic variation
- controlled by 1/2 genes
- display in bar chart
(Eg. Gender, eye colour, blood type)
Continuous variation
- takes any value in a range
- genetic & environmental variation
- controlled by multiple genes
- display in histogram
(Eg. Leaf surface area, skin colour)
Asexual reproduction
- requires only 1 parent
- replicate their genetic material and divide by mitosis
- no mixing of genetic material
- each new organism genetically identical to parent cell (clone)
Eg. Bacteria
What organisms can reproduce asexually
- potato plants
- spider plants
- daffodils
- sea anemones
- star fish
- bacteria
Sexual reproduction
- requires 2 parents
- offspring not identical as genetically information taken from both parents
- results in variation (unique genome)
Eg. Most animals/plants
describe sexual reproduction in animals
- organisms produce sex cells = gametes (male: sperm, female: ova)
- gametes fuse together in fertilisation
- fertilised egg develops into offspring
Describe sexual reproduction in plants
- pollen cell (male sex cell) fuses with egg cell (female sex cell) in ovule
- to create new seed, will grow into plant
Advantages of asexual reproduction
- if parent well adapted to area,m offspring will share identical characteristics
- only 1 parent needed (animals don’t need to find partner, plants don’t require pollination) = faster reproduction
Disadvantages of asexual reproduction
- adverse changes to biotic/abiotic factors may destroy species, all organisms will be affected as no variation
Advantages of sexual reproduction
- variation in offspring leads to adaptations in species, some organisms contain adaptations required to cope with environmental pressure, can reproduce so population of species can continue
Disadvantages of sexual reproduction
- requires 2 parents = slower reproduction so few offspring produced
Diploid cells
- Normal body cells
- contain 2 sets of each chromosome
- contain 46 chromosomes
Haploid cells
- eg. Ova & sperm cells
- have 1 of each chromosome
- contain 23 chromosomes
What happens during fertilisation
- 2 haploid gamete cells join together forming a diploid cell (zygote)
- zygote divides many times by mitosis to produce new organism
- unique combination of genes in new organism as mixture of parents genetic material
Genome
All genetic material present in an organism
How are gametes produced
- By meiosis (type of cell division)
- 4 haploid cells produced from 1 diploid parent cell
- occurs in ovaries to produce ova & testes to produce sperm
First stage of meiosis
- chromosomes in diploid cells copied
- chromosomes line up along middle of cell in pairs
- members of each pair pulled to opposite ends of cell (sections of DNA swapped)
- cell divides in two
- two separate cells formed
Second stage of meiosis:
- chromosomes line up along middle of each of 2 new cells
- each chromosome pulled in half
- single copy of each chromosome goes to opposite ends of cell
- each cell divides in two
- four new haploid cells made, each genetically different from each other & parent cell
Alleles
Different forms of a gene
Dominant allele (B)
Version of a gene whose characteristics is always expressed if present in genome, only 1 copy needed
Recessive allele (b)
Version of a gene whose characteristic only expressed if 2 copes are present in genotype
Genotype
Combination of alleles present in an organism
3 types of genotypes
- homozygous dominant (BB)
- homozygous recessive (bb)
- heterozygous (Bb)
How did Gregor Mendel discover how characteristics are inherited
- carried out experiments using pea plants
- pea plants can produce pods that are green/yellow
- green = dominant, yellow = recessive
Why does the father determine the sex of its offspring
Male gametes can have either an X or Y chromosome whereas all female gametes contain an X chromosome
23rd pair of chromosomes = sex chromosomes:
Female = XX
Male = XY
Mutation
When the sequence of DNA bases is altered
Genetic variant
- Different version of an allele, caused by change in DNA
- all arise from mutations
What determines the effect the mutation will have on an organism
The position of the mutation in the DNA sequence
What affects do mutations have on an organism
- most mutations won’t affect organism’s phenotype
- some mutations may influence organisms phenotype
- few mutations will determine organism’s phenotype, lead to variation within a species
Harmful mutations cause:
- cancer (cells grow & divide uncontrollably)
- production of abnormal protein channels (allow molecules to transport through cell membrane) that don’t function properly (eg. cystic fibrosis)
- different shaped protein molecules (eg. sickle cell anaemia = unusually shaped haemoglobin molecules, blood cells sickle shaped)
Give an example of a neutral mutation (no benefit or harm)
Ability to roll your tongue
Give an example of a beneficial mutation
Mutations in some bacteria enable them to be resistant to antibiotics, increases chance of survival
How can mutations alter an organism’s phenotype, what can this lead to
- in gene, DNA bases may be changed, added, deleted = changes sequence of bases
- order of bases in mRNA (transcription) different = different order of amino acids = wrong protein produced / fold incorrectly
- if mutation occurs in non-coding section of DNA (triggers process of transcription), gene may not be transcribed into mRNA = proteins won’t be produced
What may happen as a result of the proteins not being produced properly due to mutations
- if protein is an enzyme, active site may change shape
- can no longer bing to substrate & catalyse specific chemical reactions
- results in metabolic diseases
(eg. phenylketonuria, PKU = phenylalanine can’t be broken down by body = brain damage)
Give the years & stages of the history of genetics
1866: Discovery that certain characteristics are inherited
1869: Nuclein discovered
1944: Genes can be transferred from 1 generation to next
1950: DNA base pairs discovered
1952: DNA crystals photographed
1953: Double-helix structure of DNA identified
1953-2000: Advances in genetics
2003: Human genome project complete
Describe Gregor Mendel discoveries in 1866
Carried out experiments on peas, noticed that:
- characteristics in plants were determined by hereditary units (now called genes)
- hereditary units are passed on from both parents, 1 unit from each
- hereditary units are dominant or recessive
