Biology: Sexual Reproduction And Meiosis Flashcards
What is sexual reproduction?
Where genetic information from two organisms is combined to produce offspring which are genetically different from their parents
In sexual reproduction, what cells are used to make a child?
Gametes - 23 chromosomes (haploid)
What happens at fertilisation?
Male gamete fuses with female gamete to produce fertilised egg (a zygote) this zygote has a full set of 46 chromosomes (diploid)
What happens to a zygote after fertilisation?
Cell division by mitosis, and it develops into an embryo
What will a embryo inherit from it’s parents?
Characteristics, as it has received a mixture of chromosomes from both
In flowering plants, where are male gametes found and where are female garages found?
Male gametes = pollen
Female gametes = bottom of stigma, in ovaries
How are gametes made?
In meiosis
What makes meiosis different from mitosis?
It doesn’t produce identical cells
Where in humans does meiosis take place?
In the reproductive organs
Give the four steps of division 1 in Meiosis
1) cell duplicates DNA
2) chromosomes line up in pairs in centre of cell. Half of these are from organisms mother, half from father
3) pairs are pulled apart, so each new cell has one copy of each chromosome
4) each new cell will have mixture of mother and fathers chromosomes. Mixing up genes like this creates genetic variation in offspring
Give the two steps of division 2 in Meiosis
1) Chromosomes line up again in the centre of the cell, arms of chromosomes are pulled apart
2) you get four diploid daughter cells, gametes. Each gamete has a single set of chromosome and are genetically different
What are DNA strands? What does this mean?
DNA strands are polymere, meaning they are made up of lots of repeating units joined together
What are the four bases of DNA
Adenine, thymine, cytosine,guanine
What is the structure of one DNA molecule?
Two strands coiled together in the shape of a double helix
How do bases link in DNA?
Each base links to a base in the opposite strand in the helix
What is the complementary base pairings?
A and T
C and G
What are complementary base pairs joined together by?
Weak hydrogen bonds
What’s a gene?
A section of DNA on a chromosome that codes for a particular protein
What is the protein a gene codes for determined by?
The sequence of bases In the gene
What does all of an organisms DNA make up?
It’s genome
Give the four steps of the practical to extract DNA from fruit cells
1) mash some strawberries and put them in a beaker containing a solution of detergent and salt. Mix well. (Detergent breaks down cell membrane, releasing DNA. Salt makes DNA stick together)
2) filter mixture to get forth and Insoluble bits of cell out
3) add ice cold alcohol to filtered mixture
4) DNA will start to come out of solution as it’s not soluble in cold alcohol. Will appear as stringy white precipitate, can be fished out with glass rod
What Are genetic diagrams used for?
To predict how different characteristics will be inherited
What controls what characteristics you develop?
The genes you inherit
What are characteristics controlled by,
Single genes, or several genes interacting
What are alleles?
Genes in two different versions
What is homozygous?
Two alleles for a gene that are the same
What is the word for having two alleles of a gene that are the same
Homozygous
What is heterozygous?
Two alleles for a gene are different
What is the word for two alleles of a gene that are different?
Heterozygous
An organism has one dominant and one recessive allele for a gene, what happens?
Dominant allele determines which characteristic is present
What must the alleles be for a organism to display a dominant characteristic?
Dominant and dominant. Or dominant and recessive
What must the alleles be for a organism to display a recessive characteristic?
Recessive and recessive
What is genotype?
A combination of the alleles you have.
What is phenotype?
What characteristics you have
What is the inheritance of a single characteristic called?
Monohybrid inheritance
What two things can be used to show how recessive and dominant traits for a single characteristic are inherited?
A punnet square and monohybrid cross diagram
Draw a punnet diagram to show the chances of a hamster having superpowers across two generations, if b makes a super powered hamster. First generation is the offspring of a normal and super powered hamster. Give the percentage chance of superpowers and normality.
3 in 4 (75%) chance of normality and 1 in 4 (25%) chance of superpowers
How many matched pairs of chromosomes are there in every human body cell? What is the 23rd pair labelled, and what does it decide?
23 matched pairs. 23rd pair is XX or XY, and they’re the two chromosomes that decide if you’re male or female
What are the Chromosomes that make someone male?
Y (XY pair)
What are the Chromosomes that make someone female?
XX
Draw Both a punnet square and genetic diagram to prove there’s an equal chance of a having a boy or a girl.
Check page 29 of Combined Science textbook
Which gamete decides the sex of the baby
The Sperm cell, it has either X or Y chromosome
What is differences between the same animal called?
Variation within a species
What two types of variation can there be?
Genetic and environmental
What is genetic variation within a species caused by?
Organisms having different alleles , leading to differences in phenotypes
What two things can genetic variation be caused by?
New alleles arising through mutations, and sexual reproduction
Where do we tend to see a lot of genetic variation? Why?
Within a population of species, due to neutral mutations and environment
Give an example of variation within a species due to environment
Plant grown in sunny windowsill = luscious green with lots of leaves because it has sunlight
Same plant grown in darkness= will be tall and spindly and yellow, and eventually super dead
What are mutations?
Changes to the base sequence of DNA
What happens when a mutation occurs within a gene?
It results in an allele, (different version of the gene)
What is a mutation with no/small effect called?
Neutral mutation
What happens when new combinations of alleles interact with each other?
They produce new phenotypes
What is the base idea of the human genome project?
To find every single human gene and figure out what they all do
What were scientists hoping to achieve through the human genome project?
Finding out what diseases people are susceptible to by looking at their genes. They can identify what genes cause disorders, and try to cure them. Suggest treatment tailored for individuals.
What are inherited disorders caused by?
The presence of one or more faulty alleles in a persons genome
What are the three drawbacks of the human enorme project
1: increased stress of knowing you’re susceptible to a nasty disease
2: gene-ism ; people with genetic problems might not want kids
3: discrimination by employers and life insurers if you’re genetically likely to get a disease
