B13 - Reproduction Flashcards
B13 - Compare and contrast sexual and asexual reproduction
Involves two organisms.
Gene mixing causes variation.
Used by larger more complex organisms e.g. mammals.
Slow.
High energy requirement.
High risk (competition for mate).
Involves one organism.
No variation.
Used by small, simple organisms e.g. bacteria.
Quick.
Low energy requirement.
Low risk (no competition).
B13 - Explain why meiosis is important for sexual reproduction.
Leads to genetic variation.
Variation will allow some organisms to survive environmental changes.
Variation increases the chances of a population surviving.
B13 - Compare and contrast meiosis and mitosis
Mitosis
Used in asexual reproduction.
Used to produce body cells.
1 nuclear division.
No variation.
Diploid.
2 genetically identical daughter cells
Meiosis
Used in sexual reproduction.
Used to produce gametes.
2 nuclear divisions.
Variation.
Haploid.
4 genetically different daughter cells.
B13 - Describe the relationship between DNA, genes and chromosomes.
DNA: a complex chemical contained within chromosomes.
Chromosomes: X shaped molecules that contain long strands of DNA.
Genes: sections of DNA that code for specific proteins.
B13 - The Human Genome project
A genome is the entire genetic makeup of an organism
In 2003 scientists from all over the world working together announced they had worked out the entire human genetic code.
Studying it allows us to:
Understand inherited disorders (Cystic Fibrosis and sickle cell)
Understand the link between genetics and disease
Understand evolution and human history
B13 - What is the difference between a genotype and phenotype?
Genotype - the genetic makeup of an individual for a particular characteristic.
Phenotype - the physical appearance of an individual for a particular characteristic.
B13 - What is an allele?
A different form of the same gene.
B13 - What is a dominant allele?
An allele that causes the phenotype to be expressed even if only one is inherited.
B13 - What is a recessive allele?
An allele that causes the phenotype to be expressed even if both alleles are inherited.
B13 - What is the difference between homozygous and heterozygous?
Homozygous: an individual with two identical alleles for a characteristic e.g. DD or dd.
Heterozygous: an individual with two different alleles for a characteristic e.g. Dd.
B13 - How to construct a genetic cross diagram (punnett square)
A punnett Square is a diagram used to predict the outcome of genetically crossing two organisms.
These organisms could be heterozygous (both the dominant and recessive allele) or homozygous (two copies of the same allele, either the dominant or recessive).
Homozygous dominant = TT (25%)
Heterozygous dominant = Tt (50%)
Homozygous recessive = tt (25%)
B13 - How is sex determined?
Whether a child is a boy or a girl is determined by the set of sex chromosomes that they inherit from their parents
Girls = XX Boys = XY
The probability of having either a boy or girl is always 50%
B13 - Inherited disorders
Polydactyly: results in extra fingers or toes - caused by a dominant allele
Cystic Fibrosis: disorder of cell membranes where substances to do not pass into or out of cells efficiently - caused by a recessive allele
B13 - Types of embryo screening
Amniocentesis:
Carried out at 15-16 weeks
Involves taking some fluid from around developing fetus
The fluid contains fetal cells, which can be used for genetic screening
Chorionic villus sampling:
Carried out at 10-12 weeks
Involves taking small tissue samples from the placenta
This provides fetal cells, which can be screened
B13 - What are the advantages of embryo screening?
Allows healthy embryos to be identified.
Reduces health care and government costs.
Helps detect known genetic disorders.
Reduces the risk of multiple pregnancies.
