Inheritance And Genes Flashcards
What does DNA stand for?
Deoxyribonucleic acid
DNA has a _________ structure
-double helix
- because it has two strands
What is a chromosome
- A long molecule of DNA found in the nucleus
- Each chromosome carries many genes
How many chromosomes are there in a typical human cell?
Humans have 23 pairs of chromosomes, so 23 x 2 = 46 chromosomes in total.
Chromosomes exist in pairs. The chromosomes in the 23rd pair are known as the
Sex chromosomes
Do women have XX or XY sex chromosomes?
XX
What is a Gene
A small section of DNA that codes for a specific protein
How does DNA code for proteins
DNA can code for proteins by coding for the sequence in which amino acids are joined together.
What does the term ‘genome’ mean?
The entire set of genetic material in an organism
What are inherited diseases
- genes that cause diseases can be inherited by offspring
What can understanding genomes of other people mean
It can tell us about the migration patterns of our ancestors.
Where are the chromosomes found in the cell?
Nucleus
Alleles are…
Alleles are the different versions of a particular gene.
Our body cells contains ___ copies of….
-Our body cells contain two copies of each chromosome
- one from our mother, and one from our father.
- This means that we also have two versions of each gene (each different version is a different allele).
Homozygous
If both alleles are the same
Alleles can be either
- dominant
- recessive
Charlie is heterozygous with one dominant allele and one recessive allele.
Which allele will be expressed?
- dominant one
In order to be expressed, how many recessive alleles must be present?
2
What is the genotype
- an individual’s collection of genes
- the two alleles present for a particular gene
What is a phenotype?
The characteristics an organism expresses’ as a result of their genotype
If a mouse has one allele for brown fur, and another allele for black fur, would they be considered homozygous or heterozygous for that gene?
Heterozygous
Do animals usually reproduce via sexual or asexual reproduction?
Sexual
Which process is used to create gametes?
Meiosis
What do we call the fusion of male of female gametes?
Fertilisation
Sexual reproduction involves…
- the combination of DNA from two different parents.
- This means that the offspring will be genetically different to either of their parents.
Sperm and egg cells are haploid cells and only have __ chromosomes
23
When a sperm fertilises the egg though, they form ____ which has ___ chromosomes
When a sperm fertilises the egg though, they form a diploid cell that has 46 chromosomes.
During sexual reproduction in plants, which two gametes fuse together?
Pollen and egg
How many parents are involved in asexual reproduction?
1
As a result of asexual reproduction, are the offspring genetically identical or genetically unique?
Genetically identical
When fungi and plants reproduce asexually, which process do they use?
Mitosis
Do bacteria reproduce via sexual or asexual reproduction?
Asexual reproduction
When bacteria reproduce asexually, which process do they use?
Binary fission
What is another name for gametes?
Sex cells
Examples of gametes
- sperm
- egg
What does the term ‘haploid’ mean?
A cell that only has half the normal amount of genetic material
Are gametes haploid cells?
Yes
How many chromosomes does a human gamete have?
23
When two haploid cells join, they form
A diploid cell
During the process of meiosis, how many times does the cell divide?
2
As a result of meiosis, how many cells are produced?
4
Are the cells produced by meiosis genetically identical to each other, or genetically unique?
Genetically unique
What is asexual reproduction
- requires 1 parent
- cells are replicated by mitosis to make genetically identical copies (or binary fission in bacteria)
- The offspring are genetically identical to the parent and each other (clones)
- It’s fast and very efficient —> so it works well in a constant environment
- an example would be budding in hydra (grows on side and snaps off to grow elsewhere)
What is the disadvantage of Asexual reproduction
- All offspring are genetically identical, therefore a disease that affects one will affect them all
- this also applies to other changes in environment (e.g. temp)
What is sexual reproduction
- each parent must make a gamete which contains half it’s genetic information
- the gametes of both parents fuse during fertilisation to produce a zygote
- the offspring are therefore a combination of the DNA of both parents - and are genetically different (unless they’re twins)
Are there gametes in Asexual production and sexual production
- Asexual production: no
- sexual production: yes
Does fertilisation take place in Asexual production and sexual production
Asexual production: no
sexual production: yes
Is there variation between offspring in Asexual production and sexual production
Asexual production: No
sexual production: Yes
What type of cell division is used in Asexual production and sexual production
- Asexual production: Mitosis / Binary fission
- sexual production: Meiosis
Describe the process of Meiosis
- first DNA is replicated
- then the cell divides twice to produce 4 genetically different cells
- each with half the parent genetic material
Where does meiosis happen
Testes, ovaries
Where does mitosis happen
Everywhere
Describe the process of fertilisation
- 300 million sperm enter vagina (many die trapped in folds or don’t get through cervix)
- Pass through cervix
- some are destroyed by phagocytes
- about half go up the correct fallopian tube
- they are activated by hormones and swim faster
- sperm uses digestive enzymes to burrow into the egg
- one sperm enters and the egg hardens to prevent other sperm getting in
- The 23 chromosome from the male and female combine and make a diploid cell
Advantages of sexual reproduction
- offspring aren’t identical to parent (disease won’t wipe all of them out)
Advantages of asexual reproduction
- requires one parent
- offspring are genetically identical to the parent (successful traits are passed on)
- very fast in a constant environment
- lots of offspring produced in less time
- energy efficient
- colonisation of local area where other organisms aren’t there
Why is it important that gametes have only 23 chromosomes
- prevents doubling of chromosome number
- two can fertilise to restore back to original number of 46
Where is DNA found
In nucleus of every cell in your body
Where is DNA contained in the nucleus
In the chromosome (46 for humans/23 in human gametes)
What is a gene
- A section of DNA that codes for one protein
- it is a sequence of bases that tell the cell how to make the protein.
What is DNA made from
Nucleotides
What is a mutation
Mutation is a change in the DNA sequence (e.g. one A might become a C)
Describe the different types of mutation
- Duplication (a base in the code occurs twice)
- deletion (a base in the code goes away)
- substitution ( a base gets replaced by another)
- inversion (the sequence of bases switches around)
explain how genetic disease happen
- they are as a result of a mutation in a specific allele
- they can be passed on from parent to offspring
What is cystic fibrosis
- it results in thickening of mucus in the airways and also in your gut which can result in problems breathing and in digestion
- it affects cell membranes
- it is caused by a recessive allele
What is polydactyl
- It is when an individual is born with extra fingers or toes
- it is caused by a dominant allele
What is amniocentesis
- carried out at 15-16 weeks of pregnancy
- a sample of the fluid surrounding the foetus is taken and the cells in it can be tested
What is chronic villus sampling
- carried out between 10-12 weeks of pregnancy
- a sample is taken from the developing placenta and tested
Pre-implantation sampling
- some couples chose to use IVF and in this case the embryos can be screened for genetic disease before they are implanted
Advantages and disadvantage of taking no action from genetic counselling
- Adv: still a chance the baby doesn’t get it, no risk of harming baby
- DAdv: baby still has a chance that it gets it , risk of damage to baby is still there but just not increased
Advantages and disadvantage of pre natal diagnosis from chronic villus sampling and amniocentesis
- Adv: able to get feral cells and determine disease, baby doesn’t feel it
- DAdv: increases risk of miscarriage, faced with ethical decision to abort or not if baby gets the disease
Advantages and disadvantage of IVF preimplantation screening
Adv: know if it has disease, the baby hasn’t started developing yet, no need for abortion (just don’t use it), not a natural pregnancy
DAdv: expensive
Advantages and disadvantage of donor sperm / egg
Adv: disease
DAdv: baby can contact bio dad, the baby isn’t the dad’s bio baby, expensive
Why is the human genome important
- search for genes linked to different types of disease
- understanding and treatment of inherited disorders
- use in tracing human migration patterns from the past.
What is the human genome
- this is all off the genetic material found in a human
What are the arguments for embryo screening
- helps people stop suffering
- treating disorders costs tax payers and government a lot of money
- there’s laws to stop it going too far
What are the arguments against embryo screening
- implies people with genetic problems are undesirable —> lead to prejudice
- could advance to people picking the most ‘desirable’ babies
- expensive
What is embryonic screening
- In IVF, before putting embryo back you can take a cell and then analyse it for it’s genes
- allowing you to detect genetic disorders
What is the disadvantage to embryonic screening
- embryos with ‘bad’ alleles are destroyed
- it can lead to the decision to terminate pregnancy
