Reproduction in humans Flashcards
define sexual reproduction
type of reproduction
involves the production of gametes by meiosis
a gamete from each parent fuses to form a zygote
genetic information from each gamete is mixed so the resulting zygote is unique
define the term fertilisation
the fusion of gamete nuclei
what are gametes?
gametes are sex cells such as sperm and eggs in animals and humans
and pollen nucleus and ovum in plants
they contain half the number of chromosomes found in other body cells so they are haploid
how many chromosomes do human gametes contain?
23
half of the normal 46 found in other body cells because they only contain one copy of each chromosomes
define asexual reproduction
type of reproduction
involves mitosis only
produces genetically identical offspring know as daughter cells
how do the offspring look compared to their parents when produced asexualy?
they are genetically identical to the parent as there is no fusion of gametes and no mixing of genetic information
resulting in clones
what are the advantages and disadvantages of sexual reproduction?
ADVANTAGES
- allows genetic variation in offspring
- which can increase chances of survival in changing environments
- helps in evolution
- disease is less likely to affect offspring due to genetic variation
- natural selection can be speeded up by humans in selective breeding to increase food production
DISADVANTAGES
- takes time and energy to find mates - two parents needed
- difficult for isolated members of the species to reproduce
- fewer offspring are produced as more time and energy is required
what are the advantages and disadvantages of asexual reproduction?
ADVANTAGES
- the population can be increased rapidly when conditions are right
- can take advantages of environments quickly
- only one parent needed
- faster and requires less energy
DISADVANTAGES
- no genetic variation in population, offspring is identical to their parent (except from spontaneous mutations
- The population is vulnerable to changes in conditions and may only be suited for one habitat
- Disease is more likely to affect the whole population as there is no genetic variation
what is meiosis
form of cell division involved in the formation of gametes (non - identical haploid cells) in reproductive organs
chromosome number is halved
involves two divisions
what happens during the stages of meiosis?
chromosome pairs line up along the cell equator (centre of the cell)
the pair of chromosomes are separated and move to opposite poles of the cell
the side to which each chromosome is pulled is random - creating variation
chromosome number is halved
four unique haploid gametes are produced
why is meiosis important for sexual reproduction? (2)
increases genetic variation
it ensures that the zygote formed at fertilisation is diploid
describe fertilisation
gametes join together to have the normal number of chromosomes
the new cell then divides by mitosis (which increases the number of cells)
as the embryo develops cells differentiate
what is DNA?
the genetic material of the cell found in its nucleus
DNA is a polymer made up of two strands which form a double helix
the polymer is made up of monomers called nucleotides which each contain sugar and phosphate molecule as well as a base
what’s a genome?
the entire genetic material of an organism
what is a chromosome?
a long, coiled molecule of DNA that carries genetic information in the form of genes
how many chromosomes fo Human body cells have?
46
gametes have 23
define gene
a small section of DNA that codes for protein
each gene codes for a particular sequence of amino acids which make a specific protein
what are alleles?
different versions of the same gene
what is a dominant allele?
a version of a gene where only one copy is needed for it to be expressed
what is a recessive allele?
a version of a gene where 2 copies are needed for it to be expressed
what is meant when an organism is homozygous?
when an organism has two copies of the same allele (2 recessive of 2 dominant
what’s heterozygous?
when an organism has two different versions of the same gene (one dominant and one recessive)
what is a genotype?
the genes present for a trait
what is a phenotype
a visible characteristic
what is an inherited disorder and give me an exampole of it?
a disorder caused by the inheritance of certain alleles
examples
cystic fibrosis - caused by a recessive allele
what are sex chromosomes
males have an X and a Y chromosome
female have two X chromosomes
how do fungi usually reproduce?
by forming spores that can survive extreme conditions such as cold and lack of water. Both sexual meiotic and asexual mitotic spores may be produced, depending on the species and conditions.
what are the majority of genes found on the X chromosome rather than the Y chromosome?
the X chromosome is bigger than the Y so more genes are carried on it
what are mutation and what do they do?
Mutations may be caused by mistakes during cell division
or they may be caused by exposure to DNA-damaging agents in the environment
Mutations can be harmful, beneficial, or have no effect
What is cystic fibrosis?
A recessive phenotype caused by recessive alleles
resulting in lots of mucus in the lungs, digestive system and reproductive system
urethra
Tube which transports urine from the bladder to the outside of the body
Ureter
Tube which transports urine from the kidneys to the bladder
Ovaries
Organs which secrete oestrogen and progesterone into the bloodstream.
Eggs are produced, stored and then released from here once a month.
Testis
Organs which produce testosterone.
Sperm are produced here.
Ovum
The scientific term for the female gamete.
Sperm
The male gamete
haploid and diploid
haploid
a cell which has one copy of every chromosome
diploid
a cell that has two copies of every chromosome
oviduct
tube which transports egg from the ovaries to the uterus
fertilisation takes place here
uterus
where implantation and foetal development takes place
the lining of this organ is lost once a month in menstruation
its contractions help to force the baby through the vigina during child birth
cervix
narrow gap between the vigina and the uterus
diameter can dilate up to 10 cm during child birth
sperm duct
tube that transports sperm from the testis to the prostate gland
prostate gland
this gland contains a valve which controls whether urine of sperm enters urethra
placenta
a temporary organ is produced by the developing embryo as a site of exchange between the maternal and foetal blood
it prevents the mixing of mother and foetal blood but allows diffusion of gases, nutrients and waste
it also produces progesterone during pregnancy
average length of menstrual cycle
28 days
1 - 5 days in which menstruation takes place
menstruation
the breakdown and loss of the uterus lining from the vigina
ovulation
the process where the egg is released from the ovary
oestrogen
this hormone builds up
thickens
repairs the uterus wall after menstruation
its concentrated in the blood on day 14
progesterone
this hormone maintains a thick lining of the uterus
its levels drop at the end of the month causing menstruation to occur
levels remain high during pregnancy
Amniotic sac
the protective bag that surrounds a developing embryo in the womb
produces amniotic fluid
Amniotic fluid
fluid which surrounds a developing embryo
it protects it from mechanical shock
provides the right environment for the embryo to develop
and helps maintain constant temperature
Umbilical cord?
Umbilical artery?
Umbilical vein?
The structure which joins the developing foetus to the placenta
This blood vessel transports deoxygenated blood from the developing foetus to the placenta
This blood vessel transports oxygenated blood from the placenta to the developing foetus
testosterone
hormone which controls sex drive
aggression and development of the secondary sexual characteristics in males
