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Course: Middle school biology > Unit 7
Lesson 5: Reproduction and genetic variation- Sexual reproduction and genetic variation
- Sexual reproduction and genetic variation
- Genetics vocabulary
- Worked examples: Punnett squares
- Genetics vocabulary and Punnett squares
- Understand: sexual reproduction and genetic variation
- Apply: genetics vocabulary
- Apply: Punnett squares
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Genetics vocabulary
Learn about the terms allele, genotype, phenotype, dominant, recessive, heterozygous, and homozygous. Created by Sal Khan.
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- At3:45How do the scientist determine which allele is dominant or recessive allele? Was it by observation on which trait that are more likely be Phenotype in the child of the parents?(5 votes)
- In science class, normally there are so many alleles for one organism. To figure out what allele goes with what, normally in science class it is given but when scientists use information from the same organism to figure out what the dominant trait is. Most likely someone can answer this better, but I do remember asking my science teacher this same question. I believe this can be observed through noticing which trait has been more common over time since it is way more likely for a dominant trait to show rather than a recessive trait.(12 votes)
- What is the point of a Big b , like I know its for the brown hair but why can't it be a little b and stand for brown hair.(4 votes)
- Capital letter stands for Dominant gene lowercase stands for recessive gene.(10 votes)
- How can a haploid organism sexually reproduce?(4 votes)
- Haploid organisms either reproduce asexually, or they produce gametes through mitosis. Notice the use of the word "mitosis" not "meiosis". The cell already has the number of chromosomes required and doesn't need to cut it in half.
Does that help?(6 votes)
- If someone had blonde hair, but neither of their parents had blonde hair, would this be a mutation?(4 votes)
- Maybe that both parents had one chromosome for brown(for example) and one for blonde, but the child gets two blonde chromosomes. So that the parents both have brown hair but the child has blonde hair. In this case the blonde hair is not the result of a mutation.(3 votes)
- can genes be inherited from people other than the parents, like aunts or uncles?(3 votes)
- This may be a confusing answer so read carefully, If for instance your mother inherited a blonde hair gene from her mother and your aunt/uncle also inherited that blonde hair gene then it is possible you could have that gene BUT you would not inherit the gene directly from your aunt/uncle.
Happy Learning!(6 votes)
- what is mutation, why do we have mutation.(2 votes)
- A mutation occurs when there is an error made by a cell copying its own DNA. It doesn't occur often and is usually harmless.(3 votes)
- do we all have the same gen then because from Adam and Ave?(2 votes)
- I am not Christian and I believe everything was created by the Big Bang so I have no answer.(1 vote)
- Why are some things not sexually reproduce?(4 votes)
- It's evolution, no one fully understands it.(0 votes)
- ok the part that he said that's the hair color can it change if you dye yr hair?(2 votes)
- depends if ur talking about the gene for hair color then I don't think it would change if u dyed ur hair because ur just coloring a part of ur hair I'm pretty sure ur hair would still be inside ur head idk I'm not that smart but I'm sure it wouldn't change (lots of wurds)(1 vote)
- whya re they called that?(2 votes)
Video transcript
- [Instructor] We know that any sexually reproducing organism is getting DNA from both its male parent and its female parent and that's true also for human beings. You might know we have
23 pairs of chromosomes but let's zoom in on one of those pairs. So let's say this is one of
the chromosomes in a pair and let's say that this is the
other chromosome in the pair. So one came from one parent. The other came from the other parent. Chromosomes are nothing more
than bunched up strands of DNA plus other things that help package it. So let's unravel a little bit to understand how these relate to genes. And then, we'll dive into a little bit more
terminology around genetics. So you have this big, long strand of DNA and segments of this
code for different genes. Maybe this part right over here is related to how tall you become. So let's say that part right over there, that might be related to hair color. And in other videos, we talk about how these genes can essentially be translated eventually into proteins which are expressed in forms like height or hair color or eye color, or many, many, many, many other ways. But each of these chromosomes actually code, generally speaking, for the same genes. So if this one has a region
that codes for that gene, this one will as well and this one will also. The other chromosome in the
pair will also have a region that codes for this other gene. Now, as you can imagine, the genes that get
translated into the proteins that eventually are show
up in your hair color, they can come in different versions. So what we call the
different versions of a gene is an allele. So for example, from this parent, you might have gotten the allele here that would describe, let's say, blonde hair, I'll denote that with lowercase b, while from this parent, you might have gotten the allele that's associated with say, brown hair. So they're both associated
or they're both coding for the same type of protein that might play a role in hair color but they're different versions of it. So you could view an allele as versions or a version, I'll say, alleles are versions of a gene. Now, if you know which versions you have, then you're able to say,
"I know my or I know the organism's genotype." So in this situation, we know
we have the capital B allele which is for the brown hair and we have the lowercase b allele which is for the blonde hair, and so the genotype in this situation, where you actually know
what alleles you have, you would say that that
is, you have a capital B from one parent and you have the lowercase b from another parent. Now the thing you might be asking is, but what does this organism look like? How does this genotype
actually get expressed? And if you're asking that question where you're asking a
question of phenotype. Phenotype is what is expressed and this is usually
observable in some way. So the phenotype in this situation might be, and it's seldom
this simple in genetics, but we're gonna make it simple in this scenario, that if you have a brown
allele and blonde allele, that maybe the brown allele is dominant which is that if you have
even one brown allele, at the end of the day,
you're going to see brown. So I'll just write that
down for this scenario although that's not actually
going to be the case. Genetics gets a lot more
complicated than that but certain genes, certain alleles, they are that simply
dominant or recessive. Now you can imagine there's
many different genotypes based on what I just described that could result in this phenotype. You could have this genotype
that we just showed. You could get a brown
allele from both parents. Either of these genotypes
would express themselves as the phenotype brown, if we assume, and that is a big if, if we assume that this is the
dominant version of the gene or the dominant allele. If that is, then in either case, it will express itself as
the phenotype of brown. The only way you would get
blonde hair in this scenario is if you had two of the recessive gene or the recessive version of the gene or the recessive allele. This would lead to a blonde phenotype right over here. We've talked about dominant alleles. We've talked about recessive alleles and another piece of terminology that you will hear when
you talk about genetics are notions of homozygous, homozygous and/or versus heterozygous genotypes. And when people are talking about homozygous or heterozygous, they're talking about the genotype. Homozygous, you might know the
prefix homo refers to same. So this is a situation where both the alleles are
the same, same alleles, and heterozygous is a
situation where hetero, that's referring to
different, different alleles. So what would we call this
scenario right over here? We would call this a heterozygous
genotype for this gene. This would be homozygous dominant. We have two of the same dominant allele and this would be homozygous recessive. I'll leave you there. You're now armed to talk
a lot about genetics.